mi 







DAIRY FUNDAMENTALS 



OSCAR ERF 

PROFESSOR OF DAIRYING 
OHIO STATE UNIVERSITY 



0. G. CUNNINGHAM 

ASSISTANT PROFESSOR OF DAIRYING 
OHIO STATE UNIVERSITY 



Published by the Authors 

COLUMBUS, OHIO 

1911 



Copyright, 1911 
by 
OSCAR ERF and O. C. CUNNINGHAM 



©CLA30()4G9 



"A, 

TABLE OF CONTENTS. 

Division. Page. 

I. Milk 5 

II. Cream 10 

III. Butter 11 

IV. Other Milk Products 13 

V. Weig-ht and Specific Gravity of Milk and Its Products 16 

VI. Necessity for Testing Dairy Products 17 

VII. Testing Milk 18 

VIII. Testing Skim Milk, Buttermilk and Whey 28 

IX. Testing Cream 29 

X. Testing Butter and Cheese 32 

XI. Testing Ice Cream and Condensed Milk 36 

XII. Standardizing Milk and Cream 37 

XIII. Rules for Calculating Butter Fat Equivalent in Dif- 

ferent Products 47 

XIV. Detection of Adulteration in Milk 48 

XV. The Acid Tests for Milk and Cream 51 

XVI. Detection of Preservatives 55 

XVII. Bacteria in Milk 55 

XVIII. Fermentation Tests 58 

XIX. Rennet 59 

XX. Federal Standards for Dairy Products 59 

XXI. Laboratory Exercises 62 



DAIRY FUNDAMENTALS 



DIVISION ONE. 
MILK AND BUTTER FAT. 

Question. What is milk? 

Answer. Milk is the special fluid secreted by the females of 
milk giving- animals (the Class Mammalia )for the purpose of 
nourishing the young until they are capable of seeking for them- 
selves the kind of food which they can easily digest. 

Q. Of what is milk composed? 

A. Of water and milk solids. 

Q. Is water in milk any different from distilled water? 

A. No. 

Q. What are the milk solids? 

A. The milk solids are fat, milk sugar, albuminoids, and ash. 

Q. What is milk serum? 

A. Milk serum is the water and all of the solids except the fat. 

Q. What is milk fat or butter fat? 

A. It is a mixture of a number of distinct fats found in milk 
and is the chief constituent of butter. 

Q. Of what are these fats composed? 

A. Fatty acids and glycerine. 

Q. What are the different milk fats and the per cent, of each 
in butter fat? 

A. Butyrin 3.85% 

Volatile Caproin 3.60% 

Caprylin 55% 

Olein 35.00% 

Palmatin 25.70% 

Nonvolatile Myristin 20.20% 

Laurin 7.40% 

Caprin 1.90% 

Stearin l.i 



100.00% 
Q. What is a volatile fat? 

A. A fat composed of a soluble volatile fatty acid and 
glycerine. 

Q. What is a non- volatile fat? 

A. A fat composed of an insoluble non-volatile fatty acid 
and glycerine. 



6 MILK AND BUTTER-FAT 

Q. What is the chief function of butter fat when taken into 
the body? 

A. It is to produce heat and fat. 

Q. How does butter fat exist in milk? 

A. In the milk serum in the form of very minute globules. 
This is called an emulsion. These globules vary in size under nor- 
mal conditions, but average about 1/10,000 of an inch in diameter. 
It is estimated that in average milk there are 100,000,000 globules 
in a single drop. 

Q. What is milk sugar? 

A. In general appearance, milk sugar resembles confectioner's 
sugar, although it is not so sweet. When taken into the body, its 
function, like that oi fats, is to produce heat and fat. At high 
temperature, or on boiling, milk sugar caramelizes and is the prin- 
cipal cause of the peculiar scalded taste of boiled milk. In com- 
merce, milk sugar is used principally in lactated foods and in 
medicines. 

Q. What are the albuminoids? 

A. The albuminoids, commonly known as proteids, sometimes 
spoken of as protein, contain the nitrogen of milk. Their function, 
when taken into the body, is to furnish food to blood, muscle, 
tendon, hair, nails, etc. In milk they exist in two forms, namely, 
the casein and albumen. 

Q. What is casein? 

A. Casein of milk is what is commonly known as curd. Curd 
is also proteid. It is that part which curdles or clabbers when 
milk sours. Casein exists in a semi-solid state in milk and is the 
constituent which gives to cheese its peculiar character 

Q. What is albumen? 

A. Albumen is a clear, viscous substance of milk which re- 
sembles the white of egg, and coagulates by heat. It is coagulated 
by heat but not by rennet; while casein is coagulated by rennet 
but not ordinarily by heat. The scum which forms on boiled milk 
is albumen. 

Q. What is ash? 

A. The mineral constituents of milk are termed, collectively, 
the ash. When the ash is separated from the rest of the milk, it 
resembles ordinary wood ash. The ash is composed chiefly of the 
phosphates of calcium (lime), potassium, iron and magnesium, and 
the chloride of potassium and chlorides of sodium (common salt). 
The principal function of ash, when taken into the body, is to fur- 
nish food for bone and nerves. Most of the ash is in solution in 
the milk, 

Q. What are the average per cents of the different consti- 
tuents in milk? 



MILK AND BUTTER-FAT 



(Water, 87.47c 
A. Milk^ I Fat, 3.7% ( Casein, 2.7 7o 

(Total Solids, ^ ( Albuminoids, 3.2% ] 

12.6% ( Solids not fat, ] Sugar, 5.0 7o ( Albumen, .57o 

8.9% ( Ash, .770 



Q. How can you find the number of pounds of each consti- 
tuent, if the weight of milk and the per cent, of each constituent is 
given? 

A. Multiply the weight of milk by the per cent, of constituent 
and divide by one hundred. 

Example, — Give the total number of pounds of each of the 
constituents in 200 pounds of milk containing the following per 
cents : 

Per cent of 
constituent No. 
divided lbs. 
by 100 Milk 

Water 8740 X SOO = 1T4.80 pounds of water. 

Total Solids 1260 X 200 = 25.20 pounds of total solids 

Fat 0370 X 200 = 7.40 pounds of fat. 

Albuminoids 0320 X 200 = 6.40 pounds of albuminoids. 

Milk Sugar 0500 X 200 = 10.00 pounds of milk sugar. 

Ash 0070 X 200 = 1.40 pounds of ash. 

Q. Does the per cent, of constituents vary in milk? 
A. Yes. 

Q. JV[ay it vary in the milk given from day to day by the 
same cow? 

A. Yes. It may also vary morning and evening of the same 
day. 

Q. What are some causes of variation in milk of individual 
cows? 

A. 1. Treatment of the cow. 2. Health of the cow. 3. Ex- 
citement. 4. Manner of milking or change of milkers. 5. Length 
of time between milkings. 6. Length of time since calving. 7, 
Change of feed. 8. Composition of feed. 

Q. Does the average per cent, of these constituents vary 
greatly in the milk of a herd from day to day? 

A. No. The composition is quite constant in the mixed milk 
of a herd. 

Q. Why? 

A. Because a large number of cows giving milk of varying 
per cents, of solids tend to equalize the solids in the mixed milk. 
Hence, from day to day the difference of the per cent, of constitu- 
ents in milk from a herd is small compared with that of an indi- 
vidual cow. 



8 MILK AND BUTTER-FAT 

Q. What are the maximum and minimum per cents, of con- 
•stituents in milk? 

Maximum Minimum 

Water 90.69 80.32 

Fat 6.47 1.67 

Casein 4.23 1.79 

Albumen 4.44 .25 

Sugar 6.03 2.11 

Ash 1.21 .35 

Note. — This is according to Koenig's analysis, collected from 
different parts of the world, and represents a fair maximum and 
minimum ratio. In a few cases cov/s have been known to yield 14 
per cent, of butter fat in milk. 

Q. Do the per cents, of constituents of different breeds vary? 
A. Yes, to a certain extent ; but it depends upon individual 
breeding. The following table gives results found at the New 
York Experiment Station for one year : 

Total Albumin- 
Breed. Solids. Fats. oids Sugar Ash. 

Holstein-Friesian 11.80 3.46 3.39 4.84 .74 

Ayershire 12.75 3.57 4.43 4.33 .70 

Jersey 15.40 5.61 3.91 5.15 

Shorthorns 14.30 

Guernsey 14.90 5.12 3.61 5.11 .75 

Devon 14.50 4.15 3.76 5.07 .76 

Q. Do all cows of the same breed give the same per cent, of 
constituents? 

A. No. There is much variation in the per cent, of constitu- 
ents in milk from different cows of the same breed. The above 
table represents the average composition of milk of the different 
breeds. 

Q. To what extent do the solids of milk vary in the different 
months of the period of lactation? 

The following instance of the variation in the milk of an indi- 
vidual cow is probably a fair illustration : 

First month 14.00 per cent. 

Second month 13.50 per cent. 

Third month 13.47 per cent. 

Fourth month 13.46 per cent. 

Fifth month 13.75 per cent. 

Sixth month 14.00 per cent. 

Seventh month 14.18 per cent. 

Eighth month 14.33 per cent. 

Ninth month 14.83 per cent. 

From the above table it is seen that in the second, third, fourth 







Solids Albumin- Sugar 


Solids, 


Fat. 


not fat. 


oids. 


and ash 


12.60 


3.63 


8.97 


3.14 


5.83 


13.47 


3.55 


8.92 


3.07 


5.85 


12.37 


3.59 


8.78 


3.00 


5.78 


12.49 


3.78 


8.71 


3.05 


5.66 


12.67 


3.75 


8.92 


3.10 


5.82 


12.13 


4.00 


9.13 


3.36 


5.77 



MILK AND BUTTER-FAT 9 

and fifth months in the period of lactation of the average cow, the 
per cent, of solids is less than in the first, sixth, seventh, eighth and 
ninth months, but as a rule the greatest number of pounds of solids 
is found in milk given during the second, third, fourth and fifth 
months, due to the larger quantity given ; so the total number of 
pounds of solids averages about the same.* 

Q. To w^hat extent does the average monthly composition of 
milk vary? 

A. The average monthly composition is somewhat variable 
though not as much as one per cent., as the following table shows : 



Month Water. 

May 87.40 

Tune 87.53 

July 87.63 

August 87.51 

September 87.33 

October 86.87 

Q. Does the per cent, of constituents vary in the first and in 
the last milk of the same milking? 

A. The solids not fat remain quite constant, but the butter 
fats vary decidedly. An experiment with two cows at the Minne- 
sota Experiment Station brings out this point clearly, as the fol- 
lowing tables show : 

COW No. 1. 
First pint of milk. Last pint of milk. 

Total solids 9.42 19.49 

Fats 71 10.84 

Solids not fat 8.71 8.65 

Ash 68 .72 

Casein, albumen 3.44 3.51 

COAV No. 2. 

Total soHds 10.10 18.47 

Fats 1.02 9.49 

Solids not fat 9.08 8.98 

Ash .70 .74 

Casein, albumen 3,35 3.65 

Q. What is colostrum? 

A. The milk secreted directly after parturition or giving birth 
to the calf. It has a peculiar odor, color and slimy appearance. 

Q. What is the average composition of colostrum? 
A. Water 74.6 per cent. 

Fat 3.6 per cent. 

Casein 4.0 per cent. 



10 CREAM 

Albumin 13.6 per cent. 

Sugar 2.7 per cent. 

Ash 1.5 per cent. 

Q, Is colostrum essential to the young calf? 

A. Yes. It has a needed laxative effect. 

Q. Is colostrum fit for human consumption? 

A. No. 

Q. How can colostrum be detected? 

A. (a) Boiling- precipitates or coagulates the albumin. 

(b) The microscope shows large colostrum corpuscles. 
Q. How soon after parturition does the milk become normal? 
A. Usually in four or five days. In occasional cases it may 
remain abnormal for fifteen days. 

DIVISION TWO. 

CREAM. 
Q. What is cream? 

A. Cream consists of all the portions of milk after a part of 
the milk serum has been removed. Ordinarily cream is that portion 
of milk which rises to the top in a layer, upon letting milk stand 
for a time, or is separated from it by centrifugal force. Standard 
eream contains at least 18 per cent, of butter fat. 

Q. Why does cream rise on milk? 

A. Cream contains more butter fat than milk and since butter 
fat is the lightest constituent of milk, it rises for the same reason 
that wood floats on water. 

Q. How is cream separated from milk? 

A. By different systems : 

(1) The Shallow Pan System. — Milk is set in shallow pans 
for 24 to 36 hours, during which time the cream rises to the top. 

(2) The Deep Setting System. — Milk is set in deep narrow 
cans, 8 to 10 inches in width and 18 to 24 inches in depth. The 
cans are set in cold or ice water. The difference in temperature 
between the warm milk and the cold water in which it sets causes 
cream to rise rapidly in the milk, due to the fact that the extreme 
difference in temperature causes a vertical circulation at such a 
rapidity that the lighter parts of the milk are carried to the top 
with the current, and are prevented from being carried down on 
account of their lightness. 

(3) The Centrifugal System. — Cream is separated by centri- 
fugal force. The milk flows into a bowl, rotating very rapidly, 
causing the heavier constituents such as milk sugar, casein, al- 
bumen and ash, to fly to the outside, while the lighter butter fat 
flows toward the center of the bowl, carrying with it some of the 
other constituents. 

Q. What is the composition of cream? 

A. Cream (containing 18 per cent, to 30 per cent, of butter 



CREAM 11 

fat) has about the same per cent, of sugar, albuminoids and ash as 
milk. The fat varies decidedly and replaces the water in the 
cream. The per cent, of fat in cream may range from 18 per cent, 
to 80 per cent., according to the manner of skimming. An average 
cream contains about 22 per cent, of butter fat,. 69 per cent, of 
water, 3.8 per cent, of albuminoids, 4.6- per cent, of sugar, .6 per 
cent, of ash. Retail cream averages lower in butter fat. It is de- 
sirable that cream for butter-making contain about 35 per cent, of 
butter fat. 

Q. What gives the heavy consistency to some market cream 
which is low in butter fat? 

A. It may contain condensed milk, it may contain viscogen or 
it may be homogenized. 

Q. What is viscogen? 

A. It is a 50 per cent, sugar solution mixed with lime water 
forming sucrate of lime. 

Q. What is homogenized cream? 

A. " It may be cream which has been put through a homo- 
genizer, a machine which forces the cream through a small opening 
under very high pressure against a hard surface. This divides the 
fat globules so finely that the friction on the surface of the glob- 
ules is greater than the difference between the specific gravity of 
fat and milk serum and consequently they will not rise by gravity. 
The cream is rendered very viscous and appears richer than before 
homogenizing. 

Homogenized cream is sometimes made from an emulsion of 
skim milk and butter fat from butter, run through a homogenizer. 
Some ice cream makers make use of the latter since it is a cream 
product which may be had from stored goods at any time. 

DIVISION THREE. 

BUTTER. 
Q. What is butter? 

A. Butter is the pnoduct of gathering in any manner the fat 
of fresh or ripened cream or milk into a mass with a small propor- 
tion of the other milk constituents. It may or may not contain 
salt. 

Q. What is the average composition of butter? 

A. Water 13 per cent. 

Butter fat 83 per cent. 

Curd 1 per cent. 

Ash and Salt 3 per cent. 

100 per cent. 
Q. What is the variation in the per cent, of water in butter? 
A. From 6 per cent, to 16 per cent. More than 16 per cent, 
of water can be incorporated but, according to the Federal stand- 



12 BUTTER 

ard, butter containing 16 or more per cent, of water is considered 
adulterated. 

Q. What is the range in per cent, of butter fat in butter? 

A. From 82^4 per cent, to 94 per cent. Butter may contain 
less than 82y4 per cent, of fat but it is not standard butter accord- 
ing to the Federal standard. The Ohio standard calls for at least 
80 per cent, of butter fat in butter. 

Q. What is the range in per cent, of curd in butter? 

A. From .5 per cent, to 4 per cent. 

Q. What is the range in per cent, of salt in butter? 

A. From none to 8 per cent. When there is more than 4 per 
cent., part of it is undissolved and the butter is gritty. 

Q. What is the overrun in butter-making? 

A. The difference between the weight of churned butter and 
the butter fat in the milk or cream. 

Q, What causes overrun? 

A. The incorporation of water, salt, curd and ash in the proc- 
ess of churning. 

Q. What is the per cent, of overrun? 

A. The per cent, that the overrun is of the butter fat in the 
milk or cream. 

Q. How are the overrun and the per cent, of overrun calcu- 
lated? 

A. Suppose a butter maker secures 162 pounds of butter from 
450 pounds of cream testing 30 per cent, of butter fat? 

.30 X 450 = 135.00 pounds butter fat in the cream. 
162 — 135 = 27.00 pounds overrun. 
27 X 100 = 2700 
2700 ^ 135 = 20% overrun. 

Q. What is the usual per cent, of overrun? 

A. From 8 per cent, to 21.21 per cent., depending on the 
amount of water and curd incorporated. An overrun of 21.21 per 
cent, can be obtained in making standard butter containing 82^^ 
per cent, fat only when there is no loss of fat in churning. This is 
not possible in practice. 

Q. Can the amount of butter be calculated if the weight of 
the butter fat is known? 

A. Approximately, if one knows the per cent, of overrun 
usually obtained. Ordinarily in calculating the amount of butter 
that may be made from milk the overrun is counted 17 per cent, or 
about 1/6; therefore adding 17 per cent, or 1/6 to the butter fat 
would give the amount of butter. In starting with cream it is 
usually taken as 20 per cent, or 1/5. 

Q. How much butter may be made from 900 pounds of cream 
containing 30 per cent, of butter fat? 

A. .30 X 900 = 270.00 pounds of butter fat. 



OTHER MILK PRODUCTS 13 

Suppose the usual overrun secured by the butter-maker is 18 
per cent. Then 

.18 X ^"^0 = 'iS.G pounds overrun 
270 + 48.6 = 318.6 pounds butter 
or 1.18 X 270 = 318.6 pounds butter 
If we assume 30 per cent, to be the per cent, of overrun, then 
.20 X 370 = 54.00 pounds overrun 
270 + 54 = 324.00 pounds butter 
or 1.20 X 270 = 324.00 pounds butter 
or 1/5 of 270 =r 54.00 pounds overrun 

270 + 54 r= 324.00 pounds butter 
or 1 1/5 X 270 = 324.00 pounds butter 
Q. If a cov\^ gives 8,000 pounds of milk testing 5 per cent, 
butter fat in one year, how much butter fat will she produce and to 
how much standard butter containing 82^ per cent, of butter fat 
is it equivalent? 

A. .05 X 8000 = 400.00 pounds butter fat in vear 

400 X 1000 = 40,000 
40000 -h 82.5 = 484.84 pounds of standard butter con- 
taining 82^ per cent, of butter fat. 

DIVISION FOUR. 

OTHER AIILK PRODUCTS. 
Q. What is skim-milk? 

A. Skim-milk is that portion of milk remaining after cream 
is extracted; or, in other words, it is the milk serum, though it may 
contain a small per cent, of fat. The amount of fat remaining de- 
pends upon how thoroughly the milk has been separated. 

Q. Of what is skim-milk composed? 

A. Skim-milk has about the same per cent, of solids not fat 
as whole milk, except about 2 per cent, to 2^ per cent, more water, 
and a small amount of butter fat (about .1 to .3 of one per cent.) 
which cannot be practically separated from the milk. 

Q. What is skim-milk used for? 

A. In foreign countries it is largely used for human food, but 
in the United States it is mostly fed to young farm animals. Some 
of the things made from skim-milk are certain kinds of cheese, fer- 
mented milks, cold water paints, skim milk powder, patent foods 
and a material for sizing paper. Condensed skim-milk is used 
largely in ice cream making. 

Q. What function does it perform in the body? 

A. Skim-milk contains all the constituents which furnish food 
for muscle and bone, and in the same form and per cent, as that of 
whole milk. It also contains one of the constituents that produce 
beat, namely, rnilk sugar. 

Q. What is buttermilk? 

A. Buttermilk is the residue of the cream after the butter is 



14 OTHER MILK PRODUCTS 

churned. In other words, it is cream with the butter fat taken 
out of it. 

Q. What is the composition of buttermilk? 

A, Buttermilk is similar to skim-milk except in milk sugar. 
Its composition, however, like that of skim-milk, varies. Average 
butter milk contains about 9.3 per cent, solids, of which 4.6 per cent, 
is lactic acid and milk sugar, 3.7 per cent, casein and albumen, .3 
per cent, butter fat, and .7 per cent. ash. Buttermilk, like skim- 
milk, is used for human food, for feeding young animals, and, to a 
small extent, is used in manufacturing buttermilk cheese. It is 
also used for medicinal purposes, and is considered one of the most 
wholesome drinks. 

Q. How is artificial buttermilk prepared? 

A. By heating skim-milk to 165 deg. F. for at least 10 min- 
utes, cooling to 70 deg-. F., and adding 5 to 10 per cent, of good 
starter or culture of lactic acid bacteria. As soon as the milk has 
coagulated it is cooled to about 50 deg. to 55 deg. F. It is then 
placed in a churn and churned for five minutes or until well emul- 
sified. 

Q. How are fermented milks prepared? 

A. Skim-milk is pasteurized, then cooled, and a culture of 
acid producing bacteria added. Bacillus Bulgaricus is much used 
for this purpose in connection with other varieties. Bacillus Bul- 
garicus grows best at a temperature of 85 deg. F. to 100 deg. F. 
It is capable of producing much more acid than ordinary lactic acid 
bacteria. 

Q, What is the percentage composition of cheese? 

A. Roughly speaking a well cured cheese consists of 1/3 
water, 1/3 butter fat and 1/3 curd. 

A green Cheddar cheese contains about 37 per cent, water, 34 
per cent, fat, 24 per cent, casein and 5 per cent, milk sugar, lactic 
acid and ash (chiefly salt). 

Q. How much cheese can be made from 100 pounds of milk? 

A.- From 8 to 14 pounds, the average being about 10 pounds. 
Q. Does the composition of the milk influence cheese yield? 
A. Yes. The richer the milk in fat and casein the greater the 
cheese yield. 

Q. How may approximate cheese yield be calculated? 

A. (1) When the per cent, of fat and casein in milk are 
known, (per cent, of fat + per cent, of casein) X 1.63 = yield per 
100 pounds of milk.* 

(2) When only per cent, of fat is known, (2.3 X per cent, of 
fat) -|- 1.4 = yield per 100 pounds of milk* 

Q. What is the by-product of cheese? 

A. Whey. 

*Van Slyke. 



OTHER MILK PRODUCTS 15 

Q. What is the composition of whey? 

A. Whey is composed of about 6.7 per cent, of solids, of 
which 5.7 per cent, is milk sugar, .8 per cent, albumen, .6 per cent, 
ash, and .3 per cent. fat. Whey is not so nourishing as skim-milk, 
since it is deprived of most of the albuminoids and fats. It is gen- 
erally used for the feeding of farm animals. 

Q. What is condensed or evaporated milk? 

A. Milk from which a considerable part of the water of the 
original milk has been evaporated. Some brands contain about 40 
per cent, of cane sugar in addition to the milk solids. 

Q. What is the average composition of unsweetened con- 
densed milk? 

A. Water 71 per cent., fat 8.4 per cent., proteids 7,5 per cent., 
milk sugar 11.6 per cent., and ash 1.5 per cent. 

Q. What is the average composition of sweetened condensed 
milk? 

A. Water 26.5 per cent., fat 9 per cent., proteids 8.5 per cent., 
milk sugar 13.3 per cent., ash 1.8 per cent., and cane sugar 40.9 per 
cent. 

Q. What is a milk powder? 

A. A milk that has been evaporated to dryness and then pul- 
verized. It is usually made from skim-milk, because the fat in 
whole milk tends to become rancid, while the powdered skim-milk 
will keep indefinitely. It contains about 2 to 2.5 per cent, of water. 

Q. What is malted milk? 

A. Milk that has been heated to a high temperature, partly 
evaporated and a small amount of malt added. 

Q. What is modified milk? 

A. Milk that has had its composition changed in regard to 
one or more constituents for a special purpose such as infant feed- 
ing. Lime water and barley water are often added in modifying 
for infants. 

Q. What is certified milk? 

A. Milk produced under rules prescribed and enforced by a 
Medical Milk Commission, in regard to health of cows and attend- 
ants, sanitary methods in production, bacterial content and com- 
position. 

Q. What is ice cream? 

A. According to the government standard, ice cream is a 
frozen product made from cream and sugar, with or without a 
natural flavoring, and contains not less than 14 per cent, of milk 
fat. Market cream, usually does not come up to this standard in 
butter fat. Condensed skim-milk is quite commonly used as one 
of the ingredients of commercial ice cream. Homogenized cream 
is also used by some makers. Gelatin is commonly used as a 
hinder. 



16 WEIGHT AND SPECIFIC GRAVITY 

DIVISION FIVE. 

WEIGHT AND SPECIFIC GRAVITY OF MILK AND 
ITS PRODUCTS. 

Q. .What is the weight of a gallon, quart or pint of milk? 

A. The weight of milk varies a trifle with its specific gravity, 
or the per cent, of solids. The weight of a gallon of milk is about 
8.6 pounds; of a quart, 3.15 pounds; of a pint, 1.07 pounds; or an 
eight-gallon can should hold 68.8 pounds, or a ten-gallon can 86 
pounds of milk. 

Q. How much does a gallon of skim-milk weigh? 

A. A gallon of skim-milk varies a trifle according to its speci- 
fic gravity, but practically it may be taken as 8.65 pounds. 

Q, What is meant by specific gravity? 

A. The specific gravity of a substance is the difference be- 
tween the weight of that substance and the weight of an equal vol- 
ume of distilled water. Water is always considered as one, or the 
unit with which liquids and solids of the same temperature are 
compared ; for instance : 

One gallon of water weighs 8.3 pounds ; the specific gravity is 1. 

One gallon of milk weighs 8.6 pounds ; the specific gravity 
is 1.032. 

One gallon of butter fat weighs 7.7 pounds; the specific grav- 
ity is .93. 

Hence, other conditions being equal, the weight of cream varies 
with its per cent, of butter fat. 

Q. What is the specific gravity of cream containing different 
percents of butter fat? 

A. The specific gravity of fresh separator cream, according to 
Farrington, is as follows : Cream containing 20 per cent, of butter 
fat, 1.008 ; 25 per cent., 1.002 ; 30 per cent., .996 ; 40 per cent., .996 ; 
50 per cent., .947. 

Q. Can you find the weight of a certain volume of any sub- 
stance if the specific gravity is known? 

A. Yes; by multiplying the specific gravity of the substance 
by the weight of water of equal volume. 

EXAMPLE. 

Problem 1. — Cream that contains 20 per cent, of butter fat has 
a specific gravity of 1.008 at 60° F. What is the weight of a gallon 
of this cream? 

8.3 (the weight of a gallon of water) X 1.008, (the specific 
gravity) =: 8.366 or practically 8.4 pounds. 



NECESSITY FOR BABCOCK TEST 17 

Q. If the butter fat in milk is lighter than water, what raises 
the specific gravity to 1,032? 

A. It is due to the increased proportion of solids, not fat 
(such as albuminoids, milk sugar, and ash), which are heavier than 
water. 

Q. Why must the temperature of any substance be the same 
as the temperature at which the specific gravity of water was taken? 

A. Because liquids expand upon heating and contract when 
cooled. A gallon of water at 60° F. will, upon heating to 100° F., 
increase in volume so that it will occupy more than a gallon ; hence, 
it is necessary to keep the same temperature in order to calculate 
the specific gravity of a substance. 

DIVISION SIX. 

NECESSITY FOR TESTING DAIRY PRODUCTS. 

Q. What, then, is the just method for buying or selling milk 
or cream? 

A. According to the above answers the proper way to buy 
milk and cream is by weight and the per cent, of butter fat, since 
this constituent has the greatest marketable value at the present 
time. Nearly all the milk bought from farms by creameries, cheese 
factories and condensing factories is bought by weight, but a much 
smaller amount is bought according to the butter fat. Retail deal- 
ers, as a rule, still adhere to the old method of buying by measure 
(gallons), yet many of them are establishing arbitrary standards, 
giving the amount of butter fat the milk should contain. Nearly 
all the milk and cream that is retailed for direct consumption in 
cities is sold by measure (quarts and pints), since the labor that 
is necessary to weigh into bottles costs more than is saved. Few 
city dealers guarantee the per cent, of fat in milk and cream ; hence, 
milk or cream retailed in cities in small quantities can be justly 
sold by measure, but the price should be regulated according to the 
per cent, of butter fat it contains. For illustration, milk which con- 
tains 3 per cent, of butter fat and sells for 7 cents a quart is not 
worth as much as milk which contains 4 per cent, of butter fat, 
providing the latter is as sweet and pure as the former. It is far 
more important to buy and sell cream on a basis of the butter fat 
content. Hence, if 20 per cent, cream sells for 60 cents per gallon, 
40 per cent cream should be worth $1.20 per gallon, providing the 
cream is of equal purity and sweetness. 

Q. Can the quantity of butter fat in milk or cream be regu- 
lated? 

A. Yes; the milk or cream should be tested for its butter fat 
content and then standardized according to the per cent, desired. 
(See rules for Standardizing.) 

Q. What advantages are there for knowing the per cent, of 



18 TESTING MILK 

butter fat, other than that it serves as a basis for buying and selling 
milk and cream? 

A. (1) One can determine the value of the individual cow. 
The greater the number of pounds of butter fat a cow produces 
during the year, the more valuable is the cow, providing the feed 
and care necessary to sustain her does not overbalance the value 
of butter fat. By determining the cost of the amount of feed and 
labor that is required by a certain cow, the cost of the production 
of milk or butter fat can be calculated. (2) One can determine the 
amount of butter fat lost in whey and buttermilk in the manufac- 
ture of cheese and butter. If the loss is too great, so that the busi- 
ness becomes unprofitable, the fault can be readily discovered and 
remedied. 

DIVISION SEVEN. 

TESTING MILK. 

Q. How can you test milk? 

A. By means of the Babcock test. 

Q. Can you test other dairy products by this method? 

A. Yes ; milk, cream, skim-milk, buttermilk, whey, cheese, 
:ondensed milk, ice cream and butter, 

Q. Is it practical to buy a Babcock tester? 

A. The Babcock tester is as essential in buying milk or cream 
as the scale is in buying corn. 

Q. Name the pieces of apparatus which are used in the Bab- 
cock test. 

A. (1) Centrifuge (or whirling machine), (2) graduated Bab- 
cock milk test bottle, (3) pipette, (4) acid measure and (5) dividers. 

Q. Are there any chemicals used in making the test? 

A. Yes ; one^ — commercial sulphuric acid. 

Q. What are the different steps in testing milk with the Bab- 
cock test? 

A. 1. See that the test bottles and pipettes are accurately 
calibrated (accurately marked). 

2. See that the test bottles and pipette are clean. 

3. See that the centrifuge is properly oiled and in order before 
starting. 

4. See that the sample of milk to be tested is thoroughly 
mixed. (If a composite sample follow the details as explained 
below.) 

5. See that the temperature of the sample of milk is not below 
50° F. nor above 70° F. 

6. Measure out 17.6 cubic centimeters of the milk with the 
pipette and put it into the test bottle. 



TESTING MILK 19 

7. See that the sulphuric acid is of the proper strength (sp. 
gr. 1.82 to 1.83). 

8. Measure out 17.5 cc of sulphuric acid and pour into the 
test bottle with the milk. 

9. Thoroughly mix the acid and milk. 

10. Put the mixture into the centrifuge and see that the cen- 
trifuge is balanced. 

11. Turn the centrifuge 5 minutes at the proper speed, then 
add hot water to the mixture until it reaches the base of the grad- 
uated neck. 

12. Put into centrifuge and rotate the bottle two minutes more. 

13. Fill with hot water to 7 per cent, or 8 per cent. mark. 

14. Whirl 1 minute. 

15. Remove bottles to hot water bath, with water at a tem- 
perature of 140° F. and deep enough to cover fat column. 

Q. How are milk test bottles graduated? 

A. They are graduated from to 10 per cent. Each one per 
cent, is numbered and each one per cent, space is divided into five 
parts, each representing .2 of one per cent. 

Q. What is the basis for the graduation of test bottles? 

In calculating what quantity of butter fat could be con- 
veniently read with the greatest accuracy and with the smallest 
cost, Doctor Babcock estimated that a space in a narrow glass tube 
holding two grams of water and representing 10 per cent, of a quan- 
tity of milk would best meet these conditions. Accordingly, a tube 
containing such a column of water was marked at the base and top 
of the column, and this space was divided into ten equal portions, 
representing per cents. Each division was then divided into five 
parts, each representing two-tenths of one per cent. Since this 
column of water weighs. two grams, an equal volume of butter fat 
would weigh 1.8 grams (fat having a specific gravity of approxi- 
mately .9). Then 1.8 grams represents 10 per cent, of a certain 
volume which must be 18 grams. Hence 18 grams of m'ilk is the 
proper amount to use in testing for butter fat with the Babcock 
tester. 

Q. Why are 17.6cc of milk used? 

On account of the inconvenience of weighing, these weights 
have been reduced to their equivalent volumes. Considering the 
average specific gravity of milk as 1.032, the equivalent volume of 
18 grams of milk is found to be nearly 17.44 cubic centimeters ; 
e. g., 18 -^ 1.032 = 17.44. Allowing for the small quantity that ad- 
heres to the side of the pipette, 17.6 cubic centimeters has been 
taken as the proper amount to be measured out. 

Q. Is the graduation of testing apparatus always correct? 

A. No. 



20 TESTING MILK 

Q. How is the accuracy of graduation determined? 

A. By calibration or measuring with water, mercury or a 
plunger. 

Q. How are milk test bottles caHbrated with water? 

A. See that the bottle is cleaned thoroughly. Fill the bottle 
to the zero mark with distilled water. Remove any surplus water 
from inside of neck of bottle with a strip of blotting or filter paper. 
Measure into the bottle Ice of distilled water from an accurately 
marked burette or pipette. This should fill to the 5 per cent. mark. 
One more cc of water should fill to the 10 per cent. mark. Each 
.2cc equals one per cent, on neck of bottle. 

Instead of measuring the water, the bottle filled to the zero 
mark may be balanced on a delicate scale. Then it should take 
just one gram of distilled water to fill to the 5 per cent, mark and 
2 grams to fill to the 10 per cent. mark. Each .2 gram equals 1 per 
cent, on neck of bottle. 

Q. How may test bottles be calibrated by use of mercury? 

A. See that the bottle is thoroughly cleaned and dry — espe- 
cially free from fat. The space in the Babcock test bottle between 
the zero and the ten-per-cent. mark holds just two cubic centi- 
meters. Pour two cubic centimeters of mercury (by weight 27.18 
grams) into the test bottle. Insert a smooth cork into the bottle 
until the end reaches the ten-per-cent. mark. Invert the bottle. 
If it is correctly graduated, the mercury will just reach the zero 
mark. 

Q. How may 10 per cent, bottles be calibrated by a plunger? 

A. This tester consists of nothing more than a piece of metal 
of such a size that it will displace exactly two cubic centimeters of 
liquid. It is divided into two parts, connected with a thin wire, 
and each part displaces one cubic centimeter, which is equal to 5 
per cent, on the graduated scale of the test bottle or the two parts 
are equal to 10 per cent. It is used as follows : 

Fill the bottle with milk, alcohol or water so that its highest 
point is exactly even with the mark. Slowly lower the tester into 
the bottle until the liquid rises about half way between the two 
sections. At that point should be the five-per-cent. mark. 

That point having been established, slowly lower the entire 
tester into the bottle so that the liquid rises over the top of the 
upper section about one-eighth of an inch, and if the liquid is ex- 
actly even with the ten-per-cent. mark, and was the same at the 
five-per-cent. mark, the bottle is correct. 

Before using again, the liquid adhering to the tester should be 
wiped off. See that the neck is practically free from adhering 
drops of liquid and that no air bubbles are located between the 
tester and the neck of the bottle. 

Bottles of more than one-tenth of one per cent, out of the way 
mav be considered unfit for use. 



TESTING MII.K 21 

Q. How may 8 per cent, milk bottles be calibrated? 

A. Most conveniently by distilled water, remembering- that 
each .2cc or .2 gram equals 1 per cent, on neck of bottle. 

Q. How may pipettes be calibrated? 

A. A pipette may be calibrated by filling to the mark with 
water, dropping the water into a weighed vessel and finding the 
weight of the water. A 17.6 cc pipette should deliver 17.44 grams 
of water. It may also be calibrated by dropping the water into a 
burette which has previously been filled to the 17.6 mark. The 
water from the pipette should fill the burette to the zero mark. 

Q. How may acid measures be calibrated? 

A. The acid measure need not be calibrated with extreme ac- 
curacy, since the strength of the acid and the temperature tend to 
cause a variation in the amount. 

Q. How may cream bottles be calibrated? 

A. By the use of water or mercury in the same manner as in 
whole milk bottles. It requires the same volume and weight of 
material to fill a 10 per cent, space in an 18 gram cream bottle as 
in a milk bottle. In a 9 gram cream bottle it requires only one-half 
as much. For instance 1 cc. of water will fill the 10 per cent, space 
instead of 2 cc. 

Q. How may skim-milk bottles be calibrated? 

A. The only satisfactory way to calibrate skim milk bottles 
is by the use of mercury. The skim-milk bottle is graduated on 
the same basis as the whole milk bottle. A 10 per cent, space will 
contain 3 cc of water. A one per cent, space will contain 1/10 of 
2 or .2 cc of water. The .25 per cent, space in the skim-milk 
bottle will hold .25 of 2 cc or .050 cc of water or mercury. Since 
the specific gravity of mercury is 13.6, the number of grams of 
mercury the .05 cc. space will contain is .05 X 13.6 = .680 grams. 
Weigh out .68 gram of mercury. Place this in the large tube of 
the bottle. Secure a small stiff wire and wrap enough cotton about 
the end of it to make it fit snugly the graduated tube of the bottle. 
Push wire with cotton to the base of graduated tube. Then invert 
bottle and draw wire out slowly. If the wire fits the neck tightly 
enough the mercury will follow it. The mercury should just fill 
the graduated space from to 25/100 per cent. 

Q. Why is it necessary to mix milk for testing? 

A. Because the fat rises to the top and the upper layers of the 
milk soon become richer than the lower. 

Q. What is the best way to mix milk? 

A. By pouring from one vessel to another. 

Q. How many times is it necessary to pour? 

A. At least four or five, depending on consistency of the 
cream which has raised on milk. 



22 TESTING MILK 

Q. How are 17.6 ex. of milk obtained? 

A. Immediately after the milk has been mixed, draw milk 
into a pipette above the mark indicating 17.6 cubic centimeters, 
then suddenly close the upper end of the pipette with the index 
finger. By slightly releasing the pressure, the milk is allowed to 
run down until it 'reaches the mark, when it is again stopped by 
pressing finger on pipette. It is then transferred into the test bot- 
tle and is delivered by holding the pipette at a slight angle in order 
to allow for the escape of the air which is replaced by the milk 
that flows into the bottle. Care must be taken to see that the 
index finger is dry when measuring out milk, and that all milk 
adhering to the pipette is blown into the bottle as thoroughly as 
possible. An exact amount of milk must always be taken. Special 
care must be exercised that milk of a previous sample may not be 
dropped into the bottle; also that no milk adhering to the outside 
of the pipette is discharged into the milk bottle. 

Q. What kind and amount of acid should be used? 

A. Sulphuric acid having a specific gravity of approximately 
1.82 to 1.83 should always be used. The amount needed is approxi- 
mately 17.5 cubic centimeters, depending somewhat on the tem- 
perature of the milk and acid and the strength of the acid. The 
proper temperature of the milk is from 60° F. to 70° F. for adding 
acid. If the milk is colder than 60°, more acid must be used. If 
the milk is warmer than 70°, less acid must be used. If the acid is 
too weak more acid must be used or else the milk must be heated 
higher than 70° F. If the acid is too strong less acid must be used 
or the milk must be lowered in temperature (below 50° F.). 

Q. How can one determine whether acid is of the proper 
strength and the proper amount to use? 

A. Take three or four test bottles with milk of the same qual- 
ity and temperature. Use various amounts of acid in the various 
bottles and test each bottle under the same conditions and note 
which quantity gives clearest fat column. This will be the proper 
amount required. If 17.5 c.c. gives good results the acid is of 
proper strength. A special hydrometer or acidometer has been de- 
vised for determining the specific gravity. Strong acid has specific 
gravity above 1.83, weak below 1.82 at 60° F. 

Q. If acid is too strong, may it be diluted? 

A. Yes. This must be done very cautiously, since pouring 
water suddenly into a jug or bottle of acid causes the receptacle to 
heat and burst. A safe way is to fill a small glass three-fourths 
full water, then add acid until glass is full. This mixture, which 
becomes very hot, should then be set away and cooled gradually. 
When cold, the mixture may be turned into the carboy or the re- 
ceiver. The amount of water required depends on the strength of 
the acid. It is best to start with a small quantity of water, as, for 
instance, one-half pipette of water to one gallon of acid. 

Q. How should acid be added to milk? 



TESTING MILK 23 

A. Fill 17.5 c.c. acid measure to the mark. Transfer the acid 
into the test bottle, which contains the milk, by holding the test 
bottle at an angle of 45° and pouring the acid slowl}^ so that it will 
run down the side of the neck; at the same time slowly rotating 
the test bottle so as to wash all the milk from the neck of the 
bottle. 

Q. How should acid and milk be mixed? 

A. The mixing should be done within five to seven minutes 
after the addition of the acid, since where the milk is left too long 
in contact with the acid, the casein of the milk becomes charred, 
and rises and mixes in with the fat in the graduated column. The 
mixing should be done by a rotary motion so that the curd will 
not lodge in the neck of the bottle and again influence the reading 
of the butter fat. The graduated portion of the test bottle must 
always be kept clean and free from curd. 

Q. What precaution is necessary in placing bottles in cen- 
trifuge? 

A. To see that they balance the centrifuge wdieel. If there 
is an odd number fill another bottle with water. See that the 
bottles of the same size are opposite each other. 

Q. What is the purpose of the centrifuge? 

A. To whirl the bottles. The whirling of the bottles and the 
mixture produces a pressure known as centrifugal force. This is 
illustrated by taking a pail and swinging it arm's length in a ver- 
tical circle. If the pail is kept in motion, the water will not spill 
out even though the pail is in an inverted position. The reason 
this water does not spill out is due to the outward pressure, or cen- 
trifugal force. The heavier particles will go nearest to the outside 
(because their own weight produces a greater force) and crowd 
the lighter portions toward the center. The tendency of all parti- 
cles of matter is to arrange themselves according to their weight, 
when acted upon by centrifugal force. Another illustration may 
be found in a piece of lead and a piece of cork of equal size. Tie 
each to a string of equal length and whirl them. Upon whirling 
it is found that the pull of the piece of lead is much greater than 
that of the cork, because it is heavier. Fat is the lightest con- 
stituent of the mixture of milk and acid in the test bottle, and for 
this reason it is crowded to the top, or separated out by the heavier 
particles by centrifugal force produced by whirling the centrifuge. 

Q. What should be the speed of the centrifuge? 

A. The centrifugal force of the centrifuge depends upon the 
diameter and velocity of the wheel. It is estimated that enough 
force must be generated to equal 30.65 pounds pressure on each 
bottle. The centrifugal force is increased directly in proportion 
to the increase in the diameter and directly wnth the square of the 
velocity of the centrifuge. 



24 TESTING MILK 

Q. What is the speed required for wheels of different diam- 
eters? 

A. Diam of wheel Rev. of wheel 

in inches. per minute. 

10 1074 

12 980 

14 909 

16 840 

18 800 

20 759 

22 724 

24 693 

Q. How is the speed of a power machine determined? 

A. A\'ith speed indicator, either attached or separate. 

Q. How may the speed of a hand tester be determined? 

A. By counting- the number of revolutions of the wheel to one 
turn of the handle and multiplying' by the number of turns of the 
handle. 

Q. Is heat necessary inside the centrifuge? 

A. Yes. A temperature of 140° F. 

Q. How may this be secured? 

A. By escape of steam into the chamber, in a steam driven 
tester. In a hand tester or a tester driven by power other than 
steam, a hole may be drilled in side of tester and a steam pipe con- 
nected. Pouring boiling water into bowl of hand tester will do 
some good. A hand tester should never be operated in a cold room. 

Q. What should be length of time of first run? 

A. Five minutes, except for skim-milk which requires eight 
minutes. 

Q, How is the test completed after the five minute run? 

A. At the end of the first run hot water is added to bottom of 
neck of bottles. The centrifuge is run a second time for two min- 
utes at full speed. Water is again added, this time to the 8 per 
cent, mark and the centrifuge whirled for one minute. 

Q. What should be the temperature of water for filling and 
why is it added twice? 

A. 140° F. in a steam centrifuge. If there is no means of 
keeping up heat in centrifuge bowl, use water as near boiling as 
possible. The hot water keeps the fat column liquid. Two fillings 
and two runs after the first gives two opportunities to wash sedi- 
ment from the fat and gives a clearer fat column than one filling. 

Q. What kind of water should be used to fill test bottles? 

Soft water or distilled water. Boiling hard water or adding 
small amounts of sulphuric acid will make it safe to use. 



TESTING MILK 25 

Q. What should be temperature of fat column when read? 

A. 140" F. Place bottles in water at this temperature at com- 
pletion of third run and leave for four minutes. At 140° F. the fat 
has the desired specific gravity of .9 and a higher or lower tempera- 
ture gives a high or low reading respectively. 

Q, How is the fat column read? 

A. By counting the graduated spaces between lowest point 
of fat column and extreme upper part of upper meniscus. This is 
correct because a certain amount of residual fat is not removed from 
the serum. A pair of dividers assists in reading. 

Q. How is the amount of butter fat in the milk calculated 
from the per cent, of fat? 

A. Multiply the per cent, of butter fat by the pounds of milk 
and divide by 100 as follows : If 450 pounds of milk tests 4 per 
cent, of fat, 450 X 4 or 450 X .04 = 18.00 pounds of fat. 
100 

Q. How may one be sure tests are correct? 

A. Making tests in duplicate practically assures accuracy and 
should be done whenever possible. The two tests should not vary 
more than .2 per cent. 

Q. What should be appearance of the fat column? 

A. It should have a clear amber or yellowish color and con- 
tain no sediment. Foam on the top indicates hard water used in 
filling. A drop of alcohol removes the foam. 

Q. What causes charred particles in or below fat column? 

A. 1. Too strong acid. 2. Too much acid. 3. Milk or acid 
too warm. 4. Dropping acid through the milk. 5. Not mixing soon 
enough. 

Q, What causes white particles in or below fat column? 

A. 1. Too weak acid. 2. Not enough acid. 3. Milk or acid 
too cold. 4. Insufficient mixing. 5. Low speed of centrifuge. 

Q. How are bottles marked to distinguish them while in 
tester? 

A. With a lead pencil on etched surface on bowl of bottle. 
Glassware can be etched by the use of hydrofluoric acid, 

Q. How should the centrifuge be cared for? 

A. It should be kept clean and well oiled. It should stand 
level and be fastened to a solid foundation. A steam turbine should 
have the exhaust open wide enough to allow free escape of steam. 

Q. How should test bottles and pipettes be cleaned? 

A. Empty them while still hot to keep the fat from sticking. 
Shake them to remove sediment from bottom. Thorough rinsing 
with hot water is usually sufficient to complete the cleaning, if 
special apparatus is at hand so that the water can be introduced at 



26 TESTING MILK 

near the boiling point. It is safer to use an alkali such as salsoda, 
caustic potash or a soap powder to remove the fat. Wyandotte 
washing pow^der is good. The occasional use of a mixture of sul- 
phuric acid 1 gallon to bichromate of potash y^ to 1 pound is de- 
sirable. If a sediment collects on sides and bottom of the bottle 
put some No. 8 or No. 9 shot into the bottle with an alkali solution 
and shake vigorously. Always rinse with hot water and drain. 
Rinsing with cold water followed with hot w^ater and an occasional 
use of an alkali is sufficient for pipettes. 

Q. How is an accurate sample of a cow's milk obtained? 

A. The first milk tests very low, the last or strippings very 
high in butter fat. Therefore, the cow must be milked dry. . Then 
mix evenly by pouring from one vessel to another several times 
and take a sample from the entire milking. 

Q. How can an accurate sample of milk be secured from a 
herd? 

A. There are two ways to obtain an accurate sample of the 
milk from a herd of cows. First, mix the milk from all the cows 
together and take sample with usual precautions. Or, second, take 
equal or aliquot parts of each cow's milk and mix together in one 
sample. 

Q. What is a composite sample and how is it taken? 

A. A composite test is a test made from a number of samples 
which are taken at various times and mixed together in the right 
proportion, so that the amount of fat it contains is proportional to 
the amount of fat in the quantity of milk that it represents. To 
do this, each sample of milk taken must be an equal or aliquot part 
of each milking or of each quantity of milk. This sample can be 
taken with a brass tube of three-eights to one-half inch bore, and 
the receptacle into which the milk is placed when the sample is 
taken must ahvays be cylindrical and of the same size in order to 
secure the proportional amount of milk. The milk should be slight- 
ly stirred and the tube lowered into the milk so it will take a 
sample from the different layers of milk. The milk may be retained 
by putting the finger over the end of the tube ; then place milk in 
a jar and add a preservative to keep it sweet. A good way to se- 
cure a composite sample is to take one or more cubic centimeters 
of milk for each pound of milk in the different milkings or lots of 
milk from wdiich the composite is being taken. The preservatives 
used may be formaldehyde, corrosive sublimate, or bichromate of 
potassium. The tw^o latter substances are poisonous. The quan- 
tity of preservatives used varies with the quantity of milk to be 
preserved, and also with the temperature at which the milk is kept. 
About tw^enty to thirty drops of formaldehyde will preserve a quart 
of milk for five days at a temperature of 60° to 70° F., or 10 grains 
of corrosive sublimate or 20 grains of potassium bichromate will 
preserve the same amount of milk at the same temperature. More 
preservative should be used if more milk is added, and if kept at a 



TESTING MILK 27 

warmer temperature. Care should be taken that the jars are cov- 
ered and not exposed to too much light, for the cream bec(Dmes 
leathery and this makes it difficult to mix into the milk. To make 
a test from the composite sample, the milk must be heated to about 
110° F. in order to get a thorough mixture of cream and milk. It 
must then be gradually cooled and mixed while cooling. Care must 
be taken not to churn sample. The shaking should be done by a 
rotary motion. The sample must be taken immediately after mix- 
ing and tested in the regular manner, except where bichromate of 
potassium has been used, in which case a little less acid must be 
taken in making the test. 

Q. What is meant by an aliquot part? 

A. An aliquot part is an exact division of any number, or an 
exact per cent, of any quantity. For illustration, if a composite 
test sample is started with a rate that one thirty-third part of a 
hundred is to be taken as the sample to be tested for the butter fat, 
all other samples for this individual test must be taken in the same 
ratio. For instance, cow No. 1 gives 25 pounds of milk at a milk- 
ing; hence a proportionate quantity representing one-third of one 
peV cent., or 25 X .0033>^ = .08i^ pounds. 

At another milking she gives 20 pounds; hence, the same pro- 
portion must be taken, which is 20 X .0033J^, or .06 lbs. of the sam- 
ple to be tested. In case of taking a composite sample in a cream- 
ery, where a man brings in 800 pounds one day and 400 pounds an- 
other, he should have exactly the same per cent, of the quantity of 
milk in his composite sample bottle as he had in the milk that he 
brought, namely, twice as much in the first as in the second. 

Q. Can an accurate composite be secured by taking the same 
size sample from each of the different lots of milk regardless of 
their amount or quality? 

A. No. The following problem will illustrate this : 
A cow produces one day, 50 pounds of milk, which contains -4 
per cent, of fat. On the second day she gives but 25 pounds of 
milk which tests 3 per cent, of butter fat. If an equal amount was 
taken from these two milkings, such as with a tablespoonful, the 
sample would indicate half 3 per cent, milk and half 4 per cent, 
milk. The Babcock test would show the average per cent, fat of 
the samples which, according to their amounts, would be 3 per 
cent, and 4 per cent, added together and divided by 2, or 3^ per 
cent. Hence, 3^ times the total quantity, or 75 pounds of milk, 
would amount to 2.625 pounds of butter fat, while if an aliquot 
sample had been taken the amount of fat would.be 50 X 4 = 2.00 
and 2,5 X 3 =:. .75. Total would be 2.00 + .75 = 2.75, a difference 
of .125 of a pound of fat. 

To obtain the true per cent, of butter fat, it becomes a problem 
in alligation as, for example, in the. preceding problem, 2.75 pounds 
butter fat ~ 75 pounds milk = .0366, the average per cent, of fat 
in the above quantity of milk. Hence, from the above it will be 
seen that the only just sample that can be secured is by taking an 



28 TESTING SKIM-MILK 

aliquot part. This can be done by means of tubes and milk recep- 
tacles of the same size or relative proportionate sizes. The pro- 
portional content of a cylinder can be calculated by a formula 
ttR-H. 

7r = 3.1416. 

R = radius of cylinder or i^ diameter. 
H = heig-ht of cylinder. 
Hence the relation between two cylinders of the same height 
varies \yith the radius. 

Q. How may curdled milk be sampled for the Babcock test? 

A. When milk has curdled, the casein may be redissolved by 
adding an alkali. Powdered potash, soda or liquid ammonia may 
be used. Care should be taken not to use too much alkali as it re- 
acts with the acid and may throw some of the sample out of the 
bottle. It may at the same time cause an error in the sample by 
increasing the volume. The potash and soda may be dissolved in 
water before being used, and a volume equal to about five per cent, 
of the volume of milk will be sufficient to dissolve the casein. This 
amount of solution increases the volume of the milk, and thus 
necessarily decreases the per cent, of fat. If the volume of milk 
to be tested is measured and the solvent is also measured, the per 
cent, of decrease can be calculated in the following manner : 

Example. — Nine cubic centimeters of alkaline solution has 
been added to dissolve the casein, which is five per cent, of the 
milk used (180 :9 : : 100 :y = 5). The mixture gives a test of 3.9 
per cent, of butter fat. The test must be increased 0.195 per cent. 
(3.9 X -05 =: 0.195). Hence, the per cent, of fat in the original 
milk is 4.095 )3.9 + 0.195 = 4.095). 

Q. How may frozen milk be sampled? 

A. Frozen milk should be heated to 130° F. and then thor- 
oughly shaken and gradually cooled in order to incorporate the fat 
globules that have been churned by the freezing. 

Q. How may milk that has been churned be sampled? 

A. One method is to dissolve the little lumps of butter fat by 
adding 5 per cent, of ether and mix well. Then make a 5 per cent, 
correction in the fat. Another method is to heat the churned milk 
to a temperature of 110° to 120° F. until the fat is melted; then by 
shaking and cooling the fat can be remixed with the milk. The 
sample is then taken in the usual manner. 

DIVISION EIGHT. 

TESTING SKIM-MILK, BUTTERMILK AND WHEY. 

Q. How are skim-milk and buttermilk tested for butter fat? 

A. In the same manner as whole milk except that a special 
bottle is used, about 18 to 20 c.c. of acid is added and the centrifuge 
is whirled eight minutes for the first run instead of five minutes. 



TESTING CREAM 29 

The special skim-milk bottle has a double bore neck, one of the 
tubes being large enough to receive the milk, acid and water, the 
other being very fine and graduated for reading the fat. The whole 
graduated space represents one-fourth or 25/100 of one per cent. 
This is sub-divided into five spaces each representing 5/100 of one 
per cent. Each of these is again sub-divided into five spaces rep- 
resenting 1/100 of one per cent. If it is suspected that the skim- 
milk or'^buttermilk contains more than 25/100 per cent, of butter 
fat, it is well to use a whole milk bottle as a check. 

Q. How is whey tested for butter fat? 

A. The same as skim-milk except that about 10 c.c. of acid is 
used. 

DIVISION NINE. 

.... ■ TESTING CREAM. 

Q. Is it of great importance for any farmer that produces milk 
to know how to test cream? 

A. It is very essential if he sells cream. 

Q. How may an accurate sample of cream be secured from 
the cream can? 

A. The cream should be warm enough to pour readily. When 
it is practical to do so the cream should be poured from one vessel 
to another, as in sampling milk, and a sample taken vs^ith a dipper. 
Otherwise, a strong disc of tin or tinned metal, fastened to the end 
of a stifif rod long enough to reach to the bottom of the can, should 
be used for stirring. The upper portion of the cream is richer in 
fat than the lower, the same as in milk and the stirrer should be 
moved up and down until the upper and lower portions of the 
cream are thoroughly mixed. Thorough mixing cannot be too 
strongly emphasized. Care should also be taken to scrape from 
under the bulge of the can the heavy cream which collects there. 
If the disc used in stirring is concave the sample may be taken 
with it. 

Q. Are sampling tubes satisfactory for sampling cream? 

A. No. 

Q. Can frozen cream be sampled? 

A. Yes. If all the particles of ice are first melted. 

Q. Can churned cream be sampled? 

A. No. 

Q. Is it as satisfactory to take composite samples of cream 
as to test each sample separately? 

A. No. Because it is not usually convenient to take com- 
posites of cream proportionately or by aliquot parts. 

Q. Will the test of a composite sample of cream increase as 
it gets older? 



30 TESTING CREAM 

A. Yes. Unless very tightly stoppered and kept in a cool 
place. The same is true of milk samples but does not amount to 
so much because of the smaller per cent, of fat. 

Q, Is the testing of cream by composite samples to be rec- 
onumended ? 
A. No. 
Q. How is a cream sample prepared for testing? 

A. If cream is in good condition pour from one vessel to an- 
other. If it is thick warm slightly before pouring. If the sample 
is churned or has a tough layer on top, warm to 110° F. to melt 
butter fat, shake vigorously and cool to 60° F., continuing the 
shaking until cool. There is so much fat in cream that when it 
has once been separated it rises to the top too rapidly to sample 
accurately unless reincorporated as above. 

Q. How may sour cream be tested? 

A. It may be tested the same as sweet cream unless chunks 
of curd have formed. To destroy these it may be necessary to 
force the cream through a sieve, pressing the lumps through with 
the fingers. 

Q. How does testing cream by the Babcock test differ from 
testing milk? 

A. The cream must be accurately weighed instead of meas- 
ured. A special cream bottle is used. Less acid is required for 
cream. The fat column is not read to the top of the upper meniscus. 

Q. Why is it necessary to weigh cream? 

A. First, the Babcock test bottle has been so graduated that 
a sample to be tested should weigh 18 grams or a fraction thereof. 
Cream is lighter than milk, and thus a larger volume is required 
to weigh 18 grams. Hence, the pipette that is graduated to 17.6 
cubic centimeters, and which will discharge IS grams of milk, will 
not discharge 18 grams of cream. The greater the per cent, of fat 
in cream, the greater will be the error in the per cent, of fat by the 
use of the pipette. This can best be illustrated by a bushel of 
wheat which weighs 60 pounds. Fill the bushel measure with oats 
and you will find that it weighs 32 pounds. Comparing the bushel 
measure with the pipette, the wheat with the milk, and the oats 
with the cream, it will readily be seen that it is impossible to get 
60 pounds of oats into one bushel measure. Neither can 18 grams 
of cream be put into a 17.6 cubic centimeter pipette. 

Second, cream is apt to incorporate a great deal of air, and this 
again decreases the weight per volume. 

Third, cream is also thicker or more viscous than milk, and 
when drawn into the pipette and discharged a considerable quan- 
tity will adhere to the pipette and lessen the weight of the cream 
discharged into the bottle. Hence, for accurate work, especially 



TESTING CREAM 31 

if heavy cream is to be tested, it is necessary always to weigh the 
sample. 

Q. How is cream weighed for testing? 

A. On a delicate balance, by dropping the cream from a 
pipette after the bottles have been balanced and the proper weight 
applied. 

Q. What is the construction of the special cream bottles? 

A. V'arious types are on the market. The most satisfactory 
are the nine-inch, nine-gram 50 per cent., and the six-inch, nine- 
gram 50 per cent, bottles. The difference between these two types 
is that the neck of one is longer than that of the other and there- 
fore smaller in diameter, making accurate reading of fat column 
less difficult. These bottles are built for using a nine-gram instead 
of an eighteen-gram sample, as in the whole milk bottle. In a 
nine-gram bottle a space representing 10 per cent, on the graduated 
portion will contain one-half as much as on the eighteen-gram 
bottle, or only 1 c.c. These bottles are graduated to one-half of 
one per cent. 

Another satisfactory bottle is the nine-inch, eighteen-gram, 30 
per cent, cream bottle. As is indicated, this bottle is nine inches 
long and is built for using eighteen-gram samples, the same as a 
whole milk bottle. This bottle is graduated to .2 per cent., the 
same as a 10 per cent, whole milk bottle. Six-inch, eighteen-gram 
bottles are used, but the fat column cannot be read with the same 
accuracy as in the bottles with longer necks. 

Q. Is it necessary to use 9 grams of cream in a nine-gram 
bottle and 18 grams in an eighteen-gram bottle? 

A. No. Smaller amounts may be used. When less than 9 
grams are used in a nine-gram bottle the fat reading is corrected 
by multiplying by nine and dividing by the size of the sample. 
Example — Suppose 6.5 grams of cream are used and the fat reading 
is found to be 30.5 per cent., then (30.5 X 9) -^ 6.5 = 42.2 per cent. 
When less than 18 grams are used in an eighteen-gram, bottle, the 
same rule will hold" substituting 18 for 9. When a >4, >^ or ^4 
sample is used in either case the fat reading is corrected by multi- 
plying by 2, 3 or 4 respectively. 

Q, How much acid is added to cream in testing? 

A. Use a little less acid than cream if no water is added. If 
a sample of cream smallfer than 18 grams is used, best results are 
secured by adding enough cool water to make the total contents of 
the bottle approximately 18 grams and add acid as for milk. This 
lessens the danger of burning the fat and a clearer fat column is 
obtained than when no water is added. The bowls of some bottles 
are not large enough to add as much water as recommended above. 
It is an advantage to add at least a few c.c. in any case. A good 
rule is to add enough acid to produce a red-brown or coffee brown 
color when mixed. A rich cream does not need as much acid as a 



32 TESTING BUTTER AND CHEESE 

thin cream because there is more fat and a smaller amount of other 
solids. Too much acid will char the fat column and make the fat 
reading too low. 

Q. Can the cloudiness sometimes found in the fat column 
be overcome? 

A. Reshaking at the end of the iirst run, mixing the layer of 
fat with the acid will usually prevent this, provided the acid is of 
proper strength and the temperature in the tester is high enough. 
If the cloudiness is present at completion of the test, running an 
extra length of time in a steam heated tester will sometimes correct 
it, or the bottles may be set in cold water to solidify the fat, then 
put in hot water to heat and melt it, and run again for a few 
minutes. 

Q. Is it possible to test cream in a whole milk bottle? 

A. Yes. By making a definite dilution by weight with water 
and multiplying the fat reading at the completion of the test, by 
the number of times the cream was diluted. The dilution must be 
great enough so that the fat may be read on the 10 per cent, scale. 

Q. How should the fat column in a cream test be read? 

A. The most accurate reading is secured by adding some 
colored glymol or white mineral oil to top of fat column, as sug- 
gested in Indiana Bulletin 145. This is best added just as bottles 
are taken from hot water bath to read. Tests should always be 
read from hot water bath at 140° F. The glymol is lighter than 
the fat and remains on the top of it, destroying the meniscus. If 
glymol is not read the reading should be taken at bottom of clear 
portion of upper meniscus. 

Q. How is glymol prepared for use? 

A. In one quart of glymol suspend one ounce of crushed 
alkanet root wrapped in a piece of cheese cloth. In a day or two 
the glymol will absorb the red color from the alkanet root. The 
alkanet root can be secured from druggists. The glymol may be 
used uncolored but the line between the fat and the glymol is more 
distinct when the glymol is colored. 

DIVISION TEN. 

TESTING BUTTER AND CHEESE. 

Q. How may an accurate sample of butter for testing be 
secured? 

A. Take samples of uniform size from various parts of the 
churn or package. Place these in a vessel with tight cover. A 
glass stoppered bottle is best. Melt by holding the vessel in hot 
water. When butter becomes the cons'istency of thick cream and 
all lumps are gone, cool by holding under a stream of cold water 
and constantly agitating until it solidifies. The above operation 
furnishes a representative sample, which is uniform in composi- 



In the last sentence of the third answer on page 32, the word "read' 
should be changed to ' 'used. ' ' 



TESTING BUTTER AND CHEESE 33 

tion. The test sample is weighed from the resolidified mass. If 
one works quickly and carefully the test sample may be weighed 
from the melted sample by drawing it up in a pipette and weighing 
like cream. Great rapidity in manipulation is necessary to prevent 
error because the heavier material so quickly settles in the but- 
ter fat. 

Q. How is butter tested for butter fat? 

A. (a) Weigh 9 grams of butter into an 18-gram 50 per cent, 
cream bottle. Add 10 c.c. of hot water, then add 17.6 c.c. of sul- 
phuric acid diluted one-half. Proceed with test as for cream, mul- 
tiplying fat test by 2. 

(b) Weigh 4.5 or 5 grams of butter into a 9-gram cream 
bottle. Add about 5 to 6 c.c. of water and about a half a measure 
of one-half sulphuric acid and one-half water. Proceed with test 
as for cream. Correct the reading by multiplying by 9 and divid- 
ing by the size of sample used. If a small glass funnel is at hand 
it may be placed in top of cream bottle and balanced with it on the 
scale. Then butter may be weighed into the funnel, and run into 
the bottle by slight heating. The water and acid added to bottles 
should be poured through funnel to rinse it. 

(c) A special butter test bottle may be used. This has a 
double neck, one for adding butter and acid and one for reading 
fat column. In using this bottle 9 grams of butter are weighed into 
it, 9 grams of water are added and 9 c.c. of acid. Proceed as usual 
with the Babcock test. It is more difftcult to secure an accurate 
test of butter by the Babcock test than other dairy products. 

Q. How is butter tested for moisture by the Irish method? 

A. Prepare sample as for testing for fat. Dry an aluminum 
cup over a gas or alcohol flame, the alcohol 'flame is better. 
Then balance on delicate scale. AVeigh into the cup ten 
grams of butter. Evaporate over the alcohol flame until all water 
is gone. This point may be determined by holding a small mirror 
over the cup. When moisture ceases to condense on the mirror, 
the evaporation is complete. The sediment in cup will also turn 
a slight brown and the crackling will cease. Reweigh the cup and 
calculate the per cent, of moisture driven off. The accuracy_ of 
this test depends on gtting a fair sample of butter, careful weighing 
and evaporating to just the correct point. 

Example — Suppose a 10-gram sample of butter is used in 
either the Irish or the Farrington oven test. On reweighing the 
loss of moisture is found to be 1.4 grams. Multiply 1.4 by 100 and 
divide by 10. or 1.4 X 100 = 14 the per cent, of water in the butter. 

10 
Special moisture per cent, weights have been devised which 
will determine the per cent, of moisture without calculation. These 
are added to the side of the balance containing the sample cup after 
the evaporation and the value of weights necessary to bring to 
original weight will show per cent, of moisture driven off. 



M TESTING BUTTER AND CHEESE 

Q. Hi>w is butter tested for moisture by the oven method? 

A. AA eigh into a shallow aluminum dish from 10 to 50 grams 
of butter. The size of dish will govern the size sample used.^ The 
larger the sample the less the chance for error. Place the dish in 
the oven. Turn on enough steam to give a temperature of 250° F. 
and leave until moisture is evaporated, which will usually be from 
45 minutes to one hour. Reweigh and calculate the per cent, of 
water from the loss in weight as in the Irish test. 

Q, What is Ames-Cherry butter Moisture Test? 

A. The manipulation is the same as in the Irish test except 
that the two aluminum cups are used, the one containing the butter 
sample sitting within the other during evaporation and the two 
sitting in a paraffine bath. The advantage claimed for this test is 
that the heating may be more easily controlled. 

Q. How may the per cent, of salt in butter be determined? 

A. Prepare butter sample as usual. A method devised by 
Vivian is as follows. Weigh 3.5 grams of butter on a small piece 
of parchment paper. Add butter and paper to 180 c.c. of boiling 
water in a flask and shake to dissolve the salt, removing the stopper 
frequently to release the steam. Let stand until cool. Then by 
means of an ordinary 17.6 c.c. pipette transfer 17.6 c.c. of the fat 
free liquid to a clean beaker or white cup. The pipette may be 
forced through the layer of fat without any fat entering if the 
upper end is closed by placing the finger over it. If a separatory 
funnel is at hand the contents of the flask may be transferred to it 
before cooling and the salt solution drawn from it after the fat has 
risen. To the 17.6 c.c. of solution in the beaker add two drops of 
potassium chromate for indicator and then add a solution of silver 
nitrate from a burette until the contents of the beaker become red. 
The number of c.c. of silver nitrate solution used indicates the 
number of tenths of one per cent, of salt. For instance, if 25 c.c. of 
silver nitrate solution are used the per cent, of salt is 25 X -1 = 2.5 
per cent, of salt. The silver nitrate solution is prepared by dis- 
solving 1.018 grams of pure silver nitrate in 1 liter (1000 c.c.) of 
distilled water. 

Q. How may oleomargarine and renovated butter be disting- 
uished from butter? 

A. Melt a small piece of the suspected material in a spoon or 
other small dish over a flame. Boil vigorously. Oleo and renovat- 
ed butter sputter and crackle noisily and form little foam, while 
butter makes little noise and much foam. The oil rising on melted 
butter when allowed to stand is clear, Avhile that rising on oleo and 
renovated butter is cloudy. 

Q. How may oleomargarine and renovated butter be dis- 
tinguished? 

A. Heat about one pint of sweet skim milk to about 140° F. 
Add about a teaspoonful of the material to be tested and stir until 



TESTING BUTTER AND CHEESE 35 

it melts. Then cool quickly by setting the cup in ice water and stir 
with a wooden spatula until the fat hardens. Oleomargarine will 
collect in a lump while butter and renovated butter will remain 
separated in small granules. 

Q. What is the Hart casein test? 

A. A test for determining the per cent, of casein in milk. 

Q. What special apparatus is necessary for the Hart casein 
test? 

A. A high-geared centrifuge which will give 3,000 revolutions 
per minute for a 15-inch wheel, a special test bottle, a 5 c.c. pipette 
for measuring the milk, a cylinder for measuring the chloroform. 

Q. What principles are involved in performing the test? 

A. The casein of the milk is precipitated by a dilute solution 
of acetic acid. Chloroform is used to extract the fat and make a 
solution heavier than the milk serum. Centrifugal force is used to 
separate the chloroform containing the fat, the casein and the milk 
serum into three separate layers. 

Q. How is the acetic acid solution prepared? 

A. It must be a .25 per cent, solution. Add 10 c.c. of pure 
glacial acetic acid to 90 c.c. of distilled water, making 100 c.c. of 
solution. To 35 c.c. of this solution add 975 c.c. of distilled water, 
making 1000 c.c. This will be a .35 per cent, solution. 

Q. How is the Hart casein test made? 

A. The temperature of the milk and acetic acid must be be- 
tween 65° and 75° F., 70° F. being the temperature desired. The 
correct temperature is very important, a low temperature giving 
too high a reading of casein and a high temperature giving too low 
a reading. The room should be near 70° F. in temperature. To 
the special test bottle add 3 c.c. of best chloroform, then 20 c.c. of 
the acetic acid solution and last 5 c.c. of milk accurately measured. 
As soon as the materials are in the bottle, place the thumb over 
the opening, invert and shake somewhat vigorously for no less than 
15 seconds and no more than 30 seconds. Place the bottles in the 
centrifuge and whirl at 3,000 revolutions per minute for a 15-inch 
wheel for eight minutes. The chloroform with the fat should then 
be found in the bottom of the test bottle, the layer of white casein 
next and on top the acetic acid and milk serum. Allow the bottles 
to stand in an upright position for 10 minutes before reading. 

Q. How is a cheese sample prepared for testing? 

A. Preparing sample — As in butter great care is needed to 
secure sample representing average composition. A narrow wedge 
reaching from the edge to the center will do this. This should be 
cut quite fine with a sharp knife, taking care not to squeeze out 
moisture and fat, and thoroughl}^ mix. If a plug is taken with a 
cheese trier it should be taken perpendicularly one-third of the 
way from the edge to the center. It should reach completely 



,^6 ICE CREAM A.^D CONDENSED MILK 

through or only one-half -way through. This should be cut and 
mixed in the same manner as the wedge. It is better when it can 
be done to take two or three plugs on different sides of the cheese 
and mix the whole plugs or split them lengthwise and mix one-half 
of each. 

Q. How is cheese tested for butter fat? 

A. \\'eigh into a cream bottle 4.5 to 6 grams of the macerated 
cheese. Add about 15 c.c. of hot water and shake until the cheese 
is dissolved. Keeping the bottles warm and adding a few c.c. of 
acid will sometimes hasten the process. When the curd is dis- 
solved add acid as for cream and proceed as in testing milk. To 
correct the reading multiply by 9 or 18 depending on whether a 
9 or 18-gram bottle is used and divide by the number of grams in 
sample. 

Q. How is cheese tested for water? 

A. Prepare sample as in testing for fat. Weigh 10 grams of 
the prepared cheese into an aluminum dish. Place in an oven at a 
temperature of 250° F. for at least one hour or until weight is con- 
stant. Reweigh and calculate the per cent, of water from loss of 
weight as in testing butter for water. 

DIVISION ELEVEN. 

TESTING ICE CREAM AND CONDENSED MILK. 
Q. How may ice cream be tested for butter fat? 

A. The sample of ice cream should be melted and mixed by 
pouring from one vessel to another as with ordinary cream. Weigh 
9 grams of the ice cream into a 10 per cent, whole milk bottle. Add 
a mixture of equal parts hydrochloric acid and glacial acetic acid 
until the bottle is filled nearly to the neck. Mix and heat over a 
flame until the contents turn black. Place in centrifuge and pro- 
ceed as with milk. Correct reading by multiplying by 2. 

Q, How is unsweetened condensed milk tested for butter fat? 

A. Carefully weigh 4.5 grams of well mixed evaporated milk 
into a 10 per cent, test bottle. Add one 17.6 c.c. pipette of water. 
Add 17.5 c.c. of sulphuric acid and shake until the curd is com- 
pletely dissolved. Whirl at usual speed for five minutes. Mix 
equal parts of water and sulphuric acid in a glass beaker and fill 
test bottle to zero mark, while the mixture is still hot. Whirl for 
two minutes in tester, fill bottles to 8 per cent, mark with hot 
water and whirl for one minute. Read tests from hot water bath, 
at temperature of 140° F. reading from bottom to top of fat column 
as in whole milk. Multiply reading by 4 to secured correct per 
cent, of fat.* 

Q. How may sweetened condensed milk be tested for but- 
ter fat? 

A. By the same method as recommended for ice cream. 

*Accordins: to Hunziker. 



STANDx^RDIZING 37 

e 

DIVISION TWELVE. 

STANDARDIZING MILK AND CREAM. 

Q. "What is meant by standardizing milk or cream? 

A. To standardize milk is to bring the butter fat content to 
a given per cent, regardless of the quality of milk produced by the 
cow. If the milk as drawn from the cow contains less butter fat 
than is desired, it can be brought to the desired standard by add- 
ing cream or extracting some skim-milk. If, on the contrary, milk 
that is yielded by the cow contains more butter fat than is neces- 
sary, it can be reduced to the desired standard by extracting cream 
or adding skim-milk. 

Q. Is it just to standardize milk? 

A. Yes, because the producer can not afiford, for example, to 
produce milk containing five per cent, butter fat and receive pay 
for milk which contains only four per cent, butter fat (providing 
it is produced under equal sanitary conditions). To be legitimate 
the per cent, of fat must be indicated on the container. 

Q. Can this reduction of fat not be secured by the addition 
of water? 

A. Yes. But this is not permissible, for it also reduces the 
percentage of the solids not fat; that is, casein, milk sugar, and 
ash ; wdiereas standardizing with cream or skim-milk does not 
materially alter the proportion of solids other than butter fat. 

Q. Is there a definite standard to which milk or cream is 
standardized? 

A. The butter fat in milk or cream is increased or decreased 
to an arbitrary per cent, or standard which may be fixed by law or 
an agreement between parties in which one guarantees to furnish 
the other with a definite quantity of butter fat in every pound of 
milk or cream sold for a stated price. This price should vary with 
the per cent, of butter fat in the milk — the more butter fat for the 
same quantity of milk the higher the price, and vice versa. 

Q. How can the fat in milk or cream be reduced? 

A. If milk contains a higher per cent of butter fat than is de- 
sired, this fat can be reduced either by separating the cream out 
of a portion of the milk or by adding skim-milk. In case all the 
milk is separated for clarification, the same result may be obtained 
by mixing with the skim-milk a smaller portion of the cream than 
was contained in the original milk. Again, there may be an in- 
stance in which no skim-milk is on hand, but instead, an ample 
supply of milk with a lower per cent of butter fat .than is desired. 
This milk will answer the same purpose as skim-milk, but a larger 
proportion is required to bring the per cent down to the proper 
standard. 

Q. How can the fat in milk or cream be increased? 



38 STANDARDIZING 

A, Milk of a lower per cent, of fat than is desired may be 
standardized by taking out a portion of the skim-milk by means of 
a separator, or by adding reserved cream ; or, as in the above case, 
if the milk is separated for clarification, by mixing with the skim- 
milk a greater portion of cream than there was in the original 
milk. Here, as in the above instance, if circumstances should arise 
in which there is no cream on hand, but instead, milk of a higher 
per cent, of butter fat than the desired standard, this will then 
answer the same purpose for increasing the percentage of fat to 
the proper standard. 

Q. How can you determine the amount of skim-milk to be 
added or removed from the whole milk to obtain the desired per 
cent, of butter fat? 

A. According to the following rules : 

Rules for Standardizing Under Different Conditions Are 
as Follows : 

Rule I. 

Multiply the number of pounds of milk by the per cent, of fat 
in the milk and the product will be the number of pounds of but- 
ter fat in the milk. Divide the number of pounds of butter fat in 
the milk by the decimal representing the desired per cent, of fat, 
and the quotient will be the number of pounds of standardized 
milk.* 

Part 1. Where the Percentage of Fat is too High.^ — -From the 
number of pounds of standardized milk take the number of pounds 
of original milk and the result will be the number of pounds of 
skim-milk to be added to the original milk. 

To illustrate : 1000 pounds of milk containing 4.5 per cent, of 
butter fat are to be standardized to 4 per cent. ; how many pounds 
of milk must be added? 

Since 4.5 per cent, equals the decimal .045 then, 

1000 X -045 = 45, the number of pounds of fat in 100 pounds 
of 4.5 per cent. milk. 

45 -f- .04 = 1125, the number of pounds of 4 per cent, or stand- 
ardized milk. 

1125 ~ 1000 = 125, the amount of skim-milk to be added. 



*This answer is sufficiently' accurate for ordinary practice. As 
a matter of fact, the amount of butter fat in the cream to be stand- 
ardized is less than the amount of butter fat in the milk, on account 
of some butter fat left in the skim-milk by separating. Again, 
when skim-milk is added, butter fat is also added, the amount de- 
pending upon the amount of skim-milk added and the per cent, of 
fat contained therein. 



STANDARDIZING 39 

To formulate this problem : 
A : 1000 :: 4.5 : 4 

A =: the pounds of standardized milk. 
1000 X 4.5 

B = 1000 

4 
B = the number of pounds of skim-milk to be added. 

Part 2. Where the Percentage of Fat is too Low. — With milk 
that is to be standardized from a lower to a higher per cent, the 
same rule holds true; but in this case' take the number of pounds 
of standardized milk from the number of pounds of original milk 
and the result will be the number of pounds of skim-milk to be re- 
moved from the original milk. 

To illustrate : 1600 pounds of milk containing 3.2 per cent, of 
butter fat are to be standardized to 4 per cent. ; how much skim- 
milk must be taken from the whole milk? 

1600 X -032 = 51.2, the number of pounds of butter fat in the 
original milk. 

51.2 -:- .04 = 1280. the number of pounds of standardized milk. 

1600 — 1280 =: 320, the number of pounds of skim-milk to be 
separated from the original milk, or 
1600 X 3.2 

A = = 1280. 

4 

A ^= the number of pounds of standardized milk. 

B — 1600 — 1280 = 320. 

B = the number of pounds of skim-milk to be removed. 

Rule II. 

The same results may be reached by the following rule, which 
is often more convenient than the one above given. Divide the 
per cent, of butter fat that is in the original milk by the per cent, 
that is desired in the standardized milk. The quotient multiplied 
by the given number of pounds of milk will be the amount of 
standardized milk. If the quantity of standardized milk is greater 
than the original amount of milk the difiference must be added in 
the form of skim-milk; if less then that difiference must be separat- 
ed out as skim-milk. 

Part 1. Where the Percentage of Fat is too High. — To illu- 
strate : 200 pounds of milk containing 6 per cent, of fat are to be 
standardized to 4 per cent. ; how many pounds of skim-milk must 
be added? 

.06 -:- .04 = 1.5, hence 200 pounds of 6 per cent, milk must be 
increased by one-half with skim-milk, or to 300 pounds. The dif- 
ference between 200 pounds and 300 pounds is the amount of skim- 
milk that must be added, or 
.06 

A = — X 200, in which A = final amount of standardized milk, 
.04 



40 STANDARDIZING 

. . Part 2. Where the Percentage of Fat is too Low. — To il- 
lustrate: 652 pounds of milk containing 3.1 per cent, of butter fat 
are to be standardized to 4.5 per cent. ; how many pounds of skim- 
milk must be extracted? 

3.1 -^ 4.5 = .691, or the fractional part of 652 pounds of 3.1 per 
cent, milk to which the amount must be reduced in order to have 
the milk contain 4.5 per cent, butter fat. 

652 X .691 = 450, the number of pounds of 4.5 per cent. milk. 

652 — 450 = 202, the number of pounds of skim-milk to be re- 
moved, or 
3.1 

A = — X 652, in which A =: final amount of standardized milk. 
4.5 

Rule III. 

Occasionally there may be a quick demand for milk of a per 
cent, of fat which is not common ly produced, as is often the case 
with city dairy companies. However, milk of a known standard 
is always on hand. In this case a definite quantity of milk is want- 
ed and the exact proportions of milk or cream to be added to the 
skim-milk may be calculated in percentage or amount as follows : 

Divide the per cent, of fat in the milk that is desired by the 
per cent, of fat in the milk that is on hand. The result will be the 
per cent, of the milk on hand to be taken ; the remaining per cent. 
of milk will be the skim-milk to be used. 

To illustrate : 120 pounds of milk containing 4 per cent, of 
butter fat is desired and milk of 6 per cent, fat and skim-milk are 
on hand to be used. What per cent, of the standardized milk must 
be milk with 6 per cent, fat and what portion must be skim-milk; 
that is, how much of each must be taken in order that the mixture 
may be 4 per cent, milk? 

.04 -=- .06 r= .66^ or QQ-Zt, per cent., which is the portion of 6 
per cent, milk that the 120 pounds of standardized milk should con- 
tain. The remaining 33J^ per cent, must be skim-milk which it is 
necessary to add to bring the fat down 4 per cent. 

QGyi per cent, of 120 pounds = 80 pounds, the amount of 6 per 
cent, milk which must be mixed with 40 pounds of skim-milk to 
bring the mixture to 120 pounds of 4 per cent. milk. 

Rule IV. 

Part 1. — The actual number of pounds instead of the per cent, 
of the different kinds of milk to be added may be ascertained as fol- 
lows : Multiply the number of pounds of standardized milk desired 
by the per cent, of butter fat that the milk is to contain. This gives 
the number of pounds of butter fat in the mixture. Divide this 
amount by the per cent, of butter fat contained in the milk on hand 
and the result will be the number of pounds of that milk which the 
standardized milk should contain. The remainder would be skim- 
milk. 



STANDARDIZING 41 

To illustrate : 50 pounds of milk containing 3 per cent, fat is 
wanted, and milk containing 5 per cent, fat is to be used. 

50 X .03 = 1.5, the number of pounds of butter fat in the 3 per 
cent. milk. 

1.5 -^ .05 =: 30, the number of pounds of 5 per cent, milk which 
the standardized milk should contain. 

50 — 30 = 20, the number of pounds of skim-milk to be added. 

Part 2. — In case there is no whole milk on hand but instead 
skim-milk and cream of a known per cent, of butter fat, then the 
cream may be substituted and the fat reduced to the desired per 
cent, with skim-milk. The proportionate amounts may be calcu- 
lated as in the two foregoing methods. 

To illustrate : To make 50 pounds of milk containing 3 per 
cent, of fat or 1.5 pounds of butter fat as in the above illustration. 
If 25 per cent, cream is to be substituted for 5 per cent, milk then 
the standardized milk would have to contain 6 pounds of 25 per 
cent, cream and 44 pounds of skim milk. 

As a matter of convenience the results of the above rules calcu- 
lated on the per cent, or 100 pound basis can be tabulated in such 
a manner as to reduce the calculation to a minimum. 

Table 1 Indicates Quantity of Skim-Milk to be Added to or Sub- 
tracted from 100 Pounds of Milk to Make the 
Desired Per Cent. 



*A 
3.0 


3.25 


3.50 


3.75 


4.0 


4.25 


4.50 


4.75 


5.0 


— 7.693 


—14.285 


—20.000 


—25.000 


—29.412 


—33.333 


—36.842 


—40.000 


3.1 


— 4.616 


—11.423 


—17.333 


—22.50 


—27.059 


—31.1-11 


—34.737 


—38.000 


3.2 


— 1.539 


— 8.571 


—14.666 


—20.000 


—24.706 


—28.888 


—32.632 


—36.000 


3.3 


+ 1.539 


— 5.714 


—12.000 


—17.50 


—22.353 


— 26.666 


—30.527 


—34.000 


3.4 


-j- 4.616 


— 2.857 


— 9.333 


—15.00 


—20.000 


—24.444 


—28.422 


—32.000 


3.5 


4- 7.693 


— 0.000 


— 6.666 


—12.50 


—17.647 


—22.222 


—26.317 


—30.000 


3.6 


4-10.760 


+ 2.857 


— 4.000 


—10.00 


— 15.294 


—20.000 


— 24.212 


—28.000 


3.7 


-j-13.837 


4- 5.714 


— 1.333 


— 7.50 


—12.941 


—17.777 


—22.107 


—26.000 


3.8 


4-16.914 


4- 8.571 


+ 1.333 


— 5.00 


—10.588 


— 15.555 


—20.000 


—24.000 


3.9 


-1-19.991 


+11.428 


4- 4.000 


— 2.50 


- 8.235 


—13.333 


-17.897 


—22.000 


4.0 


4-23.068 


-^14.285 


-|- 6.666 


— 0.00 


— 5. 882 


—11.111 


—15.792 


-20.000 


4.1 


-f26.145 


-fl7.142 


-1- 9.333 


+ 2.50 


— 2.429 


— 8.888 


—13.687 


-18.000 


4.2 


-1-29.222 


+19.999 


+12.000 


-f- 5.00 


— 0.076 


— 6.666 


—11.582 


—16.000 


4.3 


4-32.299 


-j-22.856 


+14.666 


+ 7.50 


+ 0.076 


— 4.444 


— 9.477 


—14.000 


4.4 


-f35.376 


4-25.713 


+17.333 


+ 10.00 


+ 2.429 


2.222 


— 7.372 


—12.000 


4.5 


-1-38.453 


-1-28.57 


+20.000 


+12.50 


+ 5.882 


— 0.000 


— 5.267 


—10.000 


4.6 


-i-41.530 


+31.427 


+22.666 


-fIS.OO 


-|- 8.235 


+ 2.222 


— 3.162 


— 8.000 


4.7 


+44.607 


+34.284 


4-25.333 


+ 17.50 


4-10.588 


4- 4.444 


— 1.057 


— 6.000 


4.8 


+47.684 


+37.141 


-1-28.000 


-1-20.00 


+12.941 


-1- 6.666 


+ 1.057 


— 4.000 


4.9 


-1-50.761 


+39.998 


-1-30.666 


4-22.50 


4-17.647 


4- 8.888 


4- 3.162 


— 2.000 


5.0 


53.838 
*Tnr) lir 


42.855 
IP A renr 


33.333 
esents th 


25.000 
e ner cen 


20.000 
t. of fat t 


11.111 
hat i.s de.' 


+ 5.267 
ired in n 


— 0.000 
iiV 



tLeft-hand column B represents the per cent, of fat in milk on hand. 



42 STANDARDIZING 

To find the pounds of skim-milk to be added or removed, trace 
the vertical column of the per cent, of fat you desire down to where 
the horizontal column representing the per cent, of fat in the milk 
on hand intersects and the result will be the number of pounds of 
skim-milk to be added or removed, as indicated by a plus or minus 
sign before the result. 

To illustrate: If milk containing 4.5 per cent, is desired and 
milk containing 3.8 per cent, fat is on hand, then 15.5 pounds for 
every hundred pounds or 15.5 per cent, of the quantity must be 
separated out as skim-milk. 

To Standardize with Whole Milk or Cream Instead of 
Skim-Milk. 

Rule V. 

Part 1. — An instance may occur in which milk is to be raised 
to a higher per cent, with milk of a still higher per cent, of butter 
fat. The quantity to be added may be found in the following man- 
ner : From the desired per cent, of fat in the standardized milk 
subtract the per cent, of fat in the milk that is on hand which con- 
tains the lower per cent, of fat. Subtract the per cent, of fat that is 
desired in milk from the per cent, of fat in the milk that is on hand 
which contains a higher per cent, of butter fat. Divide the difit'er- 
ence between the lower per cent, and the per cent, desired by the 
difference between the higher per cent, and the per cent, desired. 
The quotient will be that part of any given quantity of milk con- 
taining the higher per cent, that should be taken. Multiply the 
quotient by the quantity of milk of the lower per cent. This will 
equal the quantity of milk of the higher per cent, to be added to 
the milk of the lower per cent, and the sum will equal the amount 
of the mixture containing the desired per cent. 

To illustrate : Standardize 20 pounds of milk containing 3 per 
cent, butter fat to 4 per cent, fat with 5.2 per cent, milk; how many • 
pounds of the latter must be added to bring the fat up to 4 per 
cent.? 

.04 — .03 = .01. 

.052 — .04= .012. 

.01 -^ .012 = 833. 

200 X .833 = 166.6, the number of pounds of 5.2 per cent, milk 
to be added. 

200 -|- 166.6 = 366.6, the number of pounds of 4 per cent, milk 
to be used. 

Part 2. — To standardize milk of a higher per cent, than is de- 
sired with milk of a lower per cent, of fat, the same rule applies ex- 
cept that the difference between the desired per cent, and the higher 
per cent, must be divided by the difference between the desired per 
cent, and the lower per cent, of butter fat. 

To illustrate : 54 pounds of milk containing 5.3 per cent, of 
butter fat are to be standardized to 4 per cent, with milk containing 
3.1 per cent, butter fat ; how many pounds of the 3.1 per cent, milk 
will be required? 



STANDx-VRDIZING 43 

.053 — .04: = .013. 

.Oi— .031 = .009. 

.013 -^ .009 = l.U. 

o-i X 1-^-i =^ ?7.?6, the number of pounds of milk containing 3.1 
^<tr cent, of fat to be added to the 54 pounds to decrease the fat 
content to -i per cent. 

Rule VI. 

To find the ratio of the number of pounds of milk of the differ- 
ent per cents., subtract the per cent, of fat in the milk of the lower 
fat content from the per cent, of fat desired in the standardized 
milk and divide this result by the 'difference between th fat per 
cents, in the milk of the higher fat content and the lower fat con- 
tent, the quotient represents the per cent, of milk of the higher fat 
content to be used in standardizing. 

To illustrate: Find the ratio of the pounds of milk for mixing 
5 with 3.5 to give 4 per cent. milk. 

4 — 3.5 = .5 

5 — 3.5 = 1.5 

.5 -^ 1.5 = .oSYs or 331/^ per cent wliich is that part oi the 
standardized milk containing 5 per cent., which is used in mixing 
with milk of 3.5 per cent, fat content. Supposing 400 pounds of 
milk of 4 per cent, butter fat is desired then 33>^ per cent, of the 
400 pounds or 133.3 pounds are to be milk containing 5 per cent, 
butter fat and 400 — 133.3 = 266. G, the number of pounds of milk 
of 3.5 per cent, butter fat that are to be taken to bring the fat con- 
tent to 4 per cent. 

Where whole milk is used for standardizing the results can be 
tabulated equally as well as when skim milk is used. In this case 
the whole milk lias a constant per cent, in each table. 

Table 2. To Standardize Cream with Milk Containing 4 
Per Cent, of Butter Fat. 
*A ir 20 22 25 27 30 

tB 
30 50.0000 61.5385 69.2308 80.3461 88.4615 100.00 

18 92.857 

19 86.666 



20 81.250 100. 

21 76.4706 94.706 

22 72.2222 88.8888 100. 

23 ' 68.4222 84.2222 94.2125 

24 65.0000 80.0000 90.0000 

25 61.905 76.1905 85.7143 

26 59.0909 72.7272 81.8181 

27 56.5217 69.5651 78.2608 

28 54.1666 66.6666 75.0000 

29 52 0000 64.0000 72.0000 

30 50.0000 61.5385 69.2308 80.3461 _ 88.4615 100.00 
*A represents the per cent, of fat that is desired in cream. 
+Left hand column B represents the per cent, of fat in cream 

on hand. 



100. 




95.4545 




91.3044 


100. 


87.5000 


95.8333 


84.0000 


92.0000 


80.3461 


88.4615 



44 STANDARDIZING 

If cream is to be standardized with whole milk the result found 
by the intersecting columns represents the pounds per hundred 
or the per cent, of the quantity which is cream of the per cent, of 
fat on hand. 

To illustrate : If cream containing" 20 per cent, of butter fat is 
desired and cream containing- 26 per cent, of butter fat is on hand 
then 72.7 per cent, of the quantity desired must be cream contain- 
ing 26 per cent, of butter fat and 27.3 per cent, of the quantity 
must be 4 per cent. milk. 

Q. How is cream standardized? 

A. The principal difference between milk and cream is that 
in cream a larger portion of the water is displaced with butter fat 
and since the variations lie mainly between the butter fat and the 
water the same methods that apply to the standardization of milk 
will apply to the standardization of cream. 

Q. What apparatus is necessary for standardizing? 

A. The apparatus necessary for standardizing milk or cream 
is a cream separator, a Babcock tester, scales, and a mixing vat, 

Q. What is the parallelogram method of standardizing? 

A. It is a method devised by Professor Pearson, formerly ot 
Cornell and may be illustrated as follows : 

A I 1 C — B or B — C 




-A or A — B 

A Per cent, of fat in milk to be mixed.' 

B Per cent, of fat in standardized milk. 

C Per cent, of fat in cream or milk to be mixed with A, 

C — B or B — ■ C Pounds of A to use. 

B — A or A — B Pounds of C to use. 

The per cent, of fat desired in the standardized mixture is al- 
ways placed in the center of the parallelogram and the per cents, of 
fat in the milks to be mixed at either of the two left hand corners. 
Then subtracting diagonally we secure the proportions of A and C 
to be mixed to secure mixture containing per cent, of fat indicated 
by B. In other words A — B or B — A depending on which is the 
larger, will give the number of pounds of C to be taken for the 
mixture. In like manner B — C or C — B will show the number 
of pounds of A to be taken for the mixture. The problems in the 
following questions will illustrate the method. 

Q. How much cream containing 30 per cent, butter fat must 
be added to milk containing 3 per cent, butter fat to standardize it 
to milk containing 5 per cent, butter fat? 

A. 3 I , 25 30 — 5) 



30 1 !2 (5 — 3) 

Placing the per cent, of fat desired in the standardized milk in 



STANDARDIZING 



45 



the center of the parallelogram and the per cents, of fat in the 
materials to be mixed at the left hand corners and subtracting 
diagonally we have 30 — 5 = 25 and 5 — 3 = 2. This means that 
the milk containing 3 per cent, butter fat and cream containing 30 
per cent, butter fat must be mixed in the proportion of 25 to 2 or 
121^ to 1, to produce milk containing 5 per cent, butter fat, that is 
for every 25 pounds of milk containing 3 per cent, butter fat in 
the mixture, there must be 2 pounds of cream containing 30 per 
cent, butter fat. Therefore, 25 : 2 : : 500 : x = 40 pounds of cream 
containing 30 per cent, butter fat t-^ add or 2 X 500 = 40 or (2 X 
500) ^ 25 = 40. ■ 25 

Q. How much milk containing 3 per cent, butter fat and 
how much cream containing 30 per cent, butter fat are to be mixed 
to secure 500 pounds of milk containing 5 per cent, butter fat? 

A. (See the parallelogram above, since the figures are the 
same.) 

25 + 2 = 27 

27 : 25 : : 500 : x =462.96 + pounds of milk containing 3 per 
cent, butter fat. 

27 : 2 : : 500 : x := 37.04 — pounds of cream containing 30 per 
cent, butter fat. 

Q. How much milk containing 3 per cent, of butter fat must 
be added to a cream containing 30 per cent, of butter fat to reduce 
the test to 25 per cent.? 

A. 30 , , 22 (25 — 3) 




5 (30 — 25) 

The cream containing 30 per cent, butter fat and the milk con- 
taining 3 per cent, butter fat must be mixed in the proportion of 
23 to 5 ; or, for every 22 pounds of cream containing 30 per cent, 
butter fat 5 pounds of milk containing 3 per cent, butter fat must 
be used. Therefore, 22 : 5 : : 500 : x"=: 113.63 = pounds of milk 
containing 3 per cent, butter fat to be added. 

500 + 113.63 = 613.63 total number of pounds of cream con- 
taining 25 per cent, butter fat secured. 

Q. How much skim-milk containing .1 per cent, butter fat 
should be added to 1000 pounds of milk containing 5.5 per cent, 
butter fat to reduce the test to 3.5 per cent.? 

A. 5.5, ,3.4 (3.5 — .1) 

I 

I 3.5 

.11 12 (5.5 — 3.5) 

The proportion should be 3.4 to 2 or 3.4 poundsof the milk 
containing 5.5 per cent, butter fat to 2 pounds of the skim-milk con- 
taining one-tenth of one per cent, butter fat. If it is desired to 
consider the skim-milk as containing no fat this can be done by 



46 BUTTER-FAT EQUIVALENT 

using in the same manner as .1 in the above example. Therefore 
3.4 : 2 :: 1000 :x = 588.33 pounds of skim-milk to add. 1000 -f 
588.23 = 1588.23 pounds of milk containing 3.5 per cent. fat. 

Q. How much milk containing 5.5 per cent, butter fat and 
how much skim-milk containing one-tenth of one per cent, butter 
fat will be needed to produce 1000 pounds of milk containing 3.5 
per cent, butter fat? 

A. (See parallelogram above.) 

3.4 + 2 = 5.4 

5.4 : 3.4 :: 1000 :x 629.6 pounds of milk containing 5.5 per 
cent, butter fat. 

1000 — 629.6 = 370.4 pounds of skim-milk containing one- 
tenth of one per cent, butter fat, or 

5.4 : 2 : : 1000 : x = 370.4 pounds of skim-milk containing one- 
tenth of one per cent, butter fat. 

Q. How much skim-milk must be removed from 780 pounds 
of milk testing 3 per cent, butter fat to increase the test to 4 per 
cent.? 

A. 3 1 3.9 pounds of milk containing 3 

per cent, butter fat to use. 




1 pounds of skim-milk to remove 
from 3.9 pounds of milk contain- 
ing 3 per cent, butter fat. 

Place the per cent, desired in the center of the parallelogram 
as usual, the per cent, of fat in milk on hand at upper left hand 
corner and per cent, of fat in skim-milk at lower left hand corner. 
Subtract diagonally as usual. The difference between the per cent, 
of fat desired and the per cent, in the skim-milk will indicate the 
number of pounds of milk containing 3 per cent, butter fat to use 
and the difference between the per cent, of fat desired and the milk 
to be skimmed will indicate the number of pounds of skim-milk to 
remove. In this problem from every 3.9 pounds of milk containing 
3 per cent, butter fat 1 pound of skim-milk must be removed to 
increase the per cent, of fat to 4. Therefore, 

3.9 : 1 :: 780 :x = 200 pounds of skim-milk to remove, or 

1 X 780 = 200 pounds of skim-milk to remove. 
3.9 

780 — 200 := 580 pounds of milk containing 4 per cent, but- 
ter fat. 

Q. How much milk containing 3 per cent, butter fat will be 
required to produce 780 pounds of milk containing 4 per cent, but- 
ter fat? 

A. (See the diagram above.) 

The 780 pounds of milk containing 4 per cent, butter fat will 
be the number of pounds of milk containing 3 per cent, butter fat 
less the number of pounds of skim-milk removed. Since 3.9 repre- 
sents the amount of milk to use and 1 the skim-milk removed. 



BUTTER-FAT EQUIVALENT 47 

3.9 — 1 or 2.9 will represent the 780 pounds of milk containing 4 
per cent, butter fat. Therefore, we have the proportion 

2.9 : 3.9 : : 780 : x = 1048.96 pounds of milk containing 3 per 
cent, butter fat to make 780 pounds of milk containing- 4 per cent, 
butter fat ; or 

3.9 X 780 = 1048.96 pounds of milk containing 3 per cent, but- 
2.9 ter fat to make 780 pounds of milk con- 

taining 4 per cent, of butter fat. 

DIVISION THIRTEEN. 

RULES FOR CALCULATING BUTTER-FAT EQUIVALENT 
IN DIFFERENT PRODUCTS. 
Q. How can the price per gallon of cream equivalent to the 
price of butter fat be found? 

A. Multiply the pounds of cream per gallon by the per cent, 
of butter fat in the cream, the product will equal the pounds of fat 
per gallon of cream. Divide the number representing the price 
per gallon of cream by the number of pounds of butter fat, the 
quotient will equal the price per pound of butter fat. 

To illustrate : What is the price per pound of butter fat if 
cream containing 20 per cent, fat sells for 50 cents per gallon? 

A gallon of 20 per cent, cream weighs approximately 8.4 
pounds. 

8.4 X -20 = 1.68 the pounds of butter fat in one gallon which 
is worth 50 cents. 

$.50 ~ 1.68 = $.297, the price of one pound of butter fat. 

Q. How can the price per gallon of cream at a certain price 
per pound of butter fat be found? 

A. Multiply the pounds of cream per gallon by the per cent, 
of fat in the cream, the product will be the number of pounds of 
butter fat in one gallon of cream. Multiply this product by the 
price per pound of butter fat you desire, the product will be the 
price per gallon for cream. 

To illustrate : At 32 cents per pound of fat what would be the 
price per gallon of cream containing 27 per cent, butter fat? 

8.3 X.27 = 2.241 pounds of fat in 1 gallon. 

2.241 X 32 = 71.712. or 72 cents, the price of the 27 per cent, 
cream. 

Q. How can the equivalent price per gallon for cream con- 
taining different per cents, of butter fat be found? 

A. This is best calculated on a basis of proportion. Divide 
the means by the extremes. 

To illustrate: If cream containing 20 per cent, butter fat is 
worth 60 cents per gallon what is cream worth containing 25 per 
cent, butter fat? 

.20 : .25 :: .60 :x 

60 X .25 = 15 

15 ^ ,20 = 75, or 75 cents, the equivalent worth of 25 per cent. 



48 DETECTION OF ADULTERATION 

cream in comparison to the worth of 20 per cent, cream at 60 cents 
a gallon. 

DIVISION FOURTEEN. 

DETECTION OF ADULTERATION IN MILK. 

Q. How can adulteration of milk with water be detected? 

A. By means of the lactometer. The Quevenne is the best, 
since it has a scale corresponding to the specific gravity of milk. 
The graduated scale from 15 to 40 being equivalent to a specific 
gravity of 1.015 to 1.040; thus a milk which has a specific gravity 
of 1.032 would show on the lactometer a reading of .32. The upper 
scale of the lactometer is a thermometer scale. These lactometers 
are to give the specific gravity at a temperature of 60° F., and as 
it is not always convenient to have the temperature of the milk 
at 60° F., when the reading is taken, corrections may be made for 
slight variations (not more than 10°) by adding to the lactometer 
reading .1 (1/10) for each degree of temperature above 60° F. or 
subtracting ,1 for each degree below 60° F. For example, the lacto- 
meter reading if 29 and the temperature 68° F., then the correct 
reading for 60° F. would be 29 + 8 = 29.8. Had fhe temperature 
been 56 degrees, the correct reading would be 29 — .4 = 28.6, and 
the specific gravity would be 1.0286. The specific gravity is ob- 
tained by prefixing 1.0 to the corrected lactometer reading. 

The reading of pure milk ranges from 28 to 34, of skim-milk 
from 33 to 36, and the specific gravity of pure milk from 1.028 to 
1.034 and of skim-milk from 1.033 to 1.036. 

The average composition of milk is as follows : 

Water 87 to 88 per cent. 

Fat 3.0 per cent, and upwards 

Solids not fat 8.5 to 9.5 per cent. 

Q. What is the function of the lactometer? 

A. The lactometer compares the weight of milk with the 
weight of an equal volume of water. Milk becomes heavier as the 
per cent, of solid not fat increases. Fat being lighter than water 
causes an error which must be taken into consideration. 

Q. What precautions are necessary in taking a lactometer 
reading? 

A. (1) Milk should stand at least one hour after milking to 
allow escape of gases. (2) The temperature must be between 50° 
and 70° F. (3) Milk should be mixed just before the reading but 
in such manner as not to cause froth or foam. (4) Milk should be 
placed in a cylinder and lactometer carefully lowered into it and 
let stand for 30 seconds and not more than one minute." (5) Read 
lactometer scale at level of milk and take thermometer reading. 
(6) Readings to one-half a lactometer degree are close enough. 

Q. How is the per cent, of solids not fat calculated? 

A. The next step to be taken is to determine the per cent, of 
fat, which is done by means of the Babcock tester. Then, having 



DETECTION OF ADULTERATION 49 

obtained the per cent, of fat and the lactometer reading, the per 
cent, of solids not fat may be calculated by the following formula : 

L -}- K 

= per cent of solids not fat. 

4 

L, Lactometer reading at 60°. 

F. Per cent, of fat. 

While the above formula is most convenient and is satisfactory 
for all practical purposes a more accurate formula is as follows- 

f- .2F rrr per cent, of solids not fat. 

4 

L. Lactometer reading at 60°. 
F. Per cent, of fat. 

Q. How is the per cent, of total solids calculated? 
A. By adding the per cent, of fat and the per cent, of solids 
not fat. 

Q. How can the per cent, of foreign water contained be 
determined? 

To find the extent to which a known sample of milk has been 
watered, multiply the per cent, of solids not fat in the adulterated 
sample by 100, and divide by the per cent, solids not fat in pure 
sample. The result will be the number of pounds of pure milk in 
100 pounds of the sample examined, and the remainder will be the 
number of pounds of water. Pure milk contains not less than 8.5 
per cent, solids not fat, and often as high as 9 and 9^ percent., and 
where it is not possible to get a sample of the pure milk for test- 
ing, use 8.5 as a standard for the first half of the season and grad- 
ually increase to 9 as the season advances and as the period of 
lactation advances. To make the foregoing more plain, take the 
following example : 

Lactometer reading 28, temperature 54°, per cent, fat 2.6, and 
suppose the pure milk to test 9 per cent, solids not fat. Find the 
per cent, of water added. 

The correct lactometer reading is 28 minus .6, or 27.4. Substi- 
tuting for formula we have : 
30.0 

27.4 _|_ 2.6 = = 7.5 per cent, solids not fat ; then 

4 
7.5 X 100 750 
— =83.3 per cent, pure milk: 

9 9 

then 100 — 83.3 = 16.6 per cent, water in the adulterated sample. 

Q. What is the specific gravity of the solids of milk? 

A. From 1.25 to 1.34 for whole milk. The specific gravity of 
the solids of completely skimmed-milk is about 1.56. _ ^ ^ 

Q. What does the specific gravity of the milk solids mdicate 
as to skimming and watering of milk? 



50 DETECTION OF ADULTERATION 

A. When the specific gravity of the milk solids is above 1.34, 
skimming is to be suspected and when it is above l.-iO it is con- 
clusive. 

Q. How may the specific gravity of milk solids be determined? 

A. By the following formula : 

t 

S = 

100s — 100 

t— ■ 

s 

S, the specific gravity of the milk solids ; s, that of the milk, 
and t, the total solids of the milk. Example. — Suppose the total 
solids of a milk were found to be 13 per cent, and the specific grav- 
ity of the milk 1.032. Then, 

(100 X 1.032) — 100 

=z 3.101 ; 13.0 — 3.101 = 9.899 ; 

1.032 
13 

■ = 1.31, the specific gravity of the milk solids. 

9.899 

Q, When is adulteration by skimming indicated? 

A. When the lactometer reading is 33 or above and the per 
cent, of fat is 3 or below, or when the lactometer reading, the spe- 
cific gravity of the milk and the per cent, of solids not fat are high 
and the per cent, of fat is low. The specific gravity of the milk 
solids is high in skim-milk. 

Q. When is adulteration by watering indicated? 

A. When the lactometer reading is 38 or below and the per 
cent, of fat is correspondingly low, or, when the lactometer read- 
ing, the specific gravit}^ of the milk, the per cent, of solids not fat 
and the per cent, of fat are low. The specific gravity of the milk 
solids is normal in watered milk. 

Q. When is adulteration by both skimming and watering in- 
dicated? 

A. When the lactometer reading and the specific gravity are 
normal or slightly below and the per cent, of solids not fat is low 
and the per cent, of fat lower in proportion than the solids not fat. 

EXAMPLE. 
27.4 is the corrected lactometer reading. 1.6 per cent, is the 
per cent, of butter fat in the above samples of milk. 27.4 is 85.6 
per cent, of 32, which is the normal specific gravity of milk, or in 
other words the sample has been reduced 14.4. Hence, if this 
sample of milk had been adulterated with water only, the per cent, 
of butter fat would be reduced proportionately ; or, for example, 
85.6 per cent, of 3 = 2.56 per cent., which should be the per cent, 
of butter with the above per cent, of dilution. However, from the 
above it will be noticed that the butter fat, 1.6 per cent., has been 
reduced 53.3 per cent., hence the difference between 85.5 and 53.3, 



TESTS FOR ACID IN MILK 51 

or 33.3 per cent, of butter fat must have been skimmed off the 
milk, aside from being adulterated. 

DIVISION FIFTEEN. 

THE ACID TEST. 

Q. What causes milk to sour on standing for eighteen to 
twenty hours at a temperature of 60° to 70° F? 

A. This change is brought about by bacteria converting the 
milk sugar of the milk into lactic acid. It generally takes about 
18 to 20 hours at 65° to 70° for them' to grow in sufficient number 
to turn the milk sour enough so that it clabbers. 

Q. Why does milk clabber? 

A. Clabbering of milk is due to the formation of lactic acid, 
which causes the casein of the milk to coagulate. 

Q. Has lactic acid any value in milk from a commercial 
standpoint? 

A. It is chiefly responsible for the flavor of butter and cheese, 
but great care must be taken in their manufacture that a proper 
amount of this acid be developed. 

Q. If too much acid is developed how would it affect the 
butter? 

A. Butter would not have such a good keeping quality and 
would not have the proper flavor. 

Q. If the acid exists in milk in solution with other liquids, 
how can the amount be readily determined? 

A. By neutralizing the acid with alkalies. 

Q. What is meant by alkalies? 

A. An alkali is a substance that has its chemical properties 
directly opposite to an acid. Either of these is a powerful agent 
for disintegrating and corroding much of the organic and inorganic 
matter, but when the two are united they lose this power. Alkalies 
are such substances as lime, lye, soda, etc. However, for testing 
purposes they must be chemically pure. Hence, if lime is added 
to sour milk, the acid unites with the lime, forming a substance 
which is neutral, neither alkaline nor acid. 

Q. Does a certain amount of alkali neutralize a certain 
amount of acid? 

A. Yes; if the per cent, of alkalinity of a solution is known, 
and the amount added to an acid substance, the per cent, of acid in 
the solution can be calculated. 

Q. How can one tell when the alkali has neutralized the acid? 

A. By means of an indicator. This indicator is colorless in 
appearance if added to the acid, but turns pink when added to 
alkali, hence if a few drops of this indicator (which is commonly 
known as phenolphthalein) be added to the milk, the same will 
remain colorless until sufficient alkali has been added to neutralize 



52 TESTS FOR ACID IN MILK 

the acid, and by adding a slight amount more the solution changes 
to a pink color. 

Q. How do you determine the acid by means of the Mann's 
test? 

A. The Mann's test consists of a 50 cubic centimeter burette, 
a 50 cubic centimeter pipette, a white porcelain cup, and a glass 
stirring rod. This alkali can be bought in gallon bottles, and is 
made by dissolving four grams of sodium hydroxide, to which 
enough distilled water is added to make one liter of solution. Each 
cubic centimeter, containing .001 of a gram of sodium hydroxide, 
will neutralize .009 of a gram of lactic acid. This is obtained from 
the fact that a normal solution of lactic acid contains 90 grams of 
acid in each liter, or 1,000 cubic centimeters. A 10th normal solu- 
tion would then contain one-tenth as much, or 9 grams to each 
liter, and a cubic centimeter, which contains .001 as much as a 
liter, would contain .009 of a gram of lactic acid. With the ap- 
paratus and solution on hand, measure 50 cubic centimeters of 
cream with a pipette into a beaker. Rinse the pipette with dis- 
tilled water adding same to the beaker. Add five drops or more of 
indicator. Fill the burette to the zero mark with neutralizer, but 
before doing this be sure and see that the burette is absolutely free 
from water and acids. Probably the best way is to rinse the 
burette with a little of this solution. Now add the solution to the 
cream in a very slow manner until you notice that the solution ap- 
pears very reluctant in destroying the pinkish color on stirring. 
Then this neutralizing solution should be added drop by drop only. 
The moment the cream remains pink, the acid has been neutralized. 
The number of cubic centimeters of alkali added to the cream i.^ 
read on the burette, and from this the percentage of acid is calcu- 
lated in the following manner : The number of cubic centimeters 
of alkali multiplied by .009, divided by the number of cubic centi- 
meters of cream, and multiplied by 100. 

Example. — It required 33 cubic centimeters of alkali to neu- 
tralize 50 cubic centimeters of cream ; what per cent, of acid is in 
the cream? 

The formula would be like this: 
32 X .009 

. X 100 = .576. 

50 

It is not essential to use 50 cubic centimeters of material. Any 
other amount may be used substituting the same for 50 in the 
above formula. When 17.6 cubic centimeters are used a result, 
accurate enough for all practical purposes may be obtained by 
dividing the cubic centimeters of alkali .by .2. Suppose 4.4 cubic 
centimeters of alkali were used to neutralize 17.6 cubic centimeters 
of milk or cream. Then 4.4 -^- .3 = .33 per cent, of acid. 

Q. How do you determine the acid by means of the Farring- 
ton Alkaline Tablet test? 



TESTS FOR ACID IN AIILK 53 

A. The Farrington Alkaline Tablet test works on the same 
principle as the Mann's test. Instead of the neutralizer being in a 
solution form, as in the Mann's test, it is put up in tablets. Dis- 
solve five tablets in enough water to make 97 cubic centimeters 
solution. The tablets must be dissolved so that it becomes a per- 
fect solution. Measure out with a Babcock pipette 17.6 cubic cen- 
timeters of the milk or cream to be tested into a white porcelain 
cup (a white cup is preferable because one can more easily see the 
pink color). Add solution to milk or cream until a permanent pink 
color is obtained, the same as in the Mann's test. Read the number 
of cubic centimeters solution used to' change the color, and this will 
indicate the number of hundredths of one per cent, of acidity in 
milk or cream. 

It is convenient to make up the Farrington solution in a 100 c.c. 
graduated cylinder fitted tightly with a stopper. Then the solu- 
tion may be poured directly from the cylinder and the c.c. used, 
read from the cylinder graduation. Example. — If it requires 50 
cubic centimeters of tablet solution to neutralize the acid of the 
cream, then the acidity would be .5 per cent. 

Q, How may acidity be estimated approximately by the Far- 
rington tablets? 

A. For some purposes it is advantageous to determine 
whether milk contains more or less than .3 per cent, of acid. The 
solution for this test is prepared by dissolving tablets at the rate 
of 2 to each ounce of water used. The test is made by mixing 
equal parts of the tablet solution and the milk to be tested in a 
white cup. If the milk remains white it contains more than .2 per 
cent, of acid while if it turns pink it contains less than .2 per cent, 
of acid. The deeper the pink color the sweeter the milk. 

Q. How can you obtain the per cent, of acidity by means of 
the Marschall test? 

A. In this acid test the neutralizer used is the regular standard 
1/10 normal alkali, which can be obtained from all dairy supply 
houses and experiment stations. 

The Marschall acid test contains the following parts : 
Combined burette and bottle for the neutralizer. 
9 cubic centimeter pipette. 
Bottle of indicator. 
Yz gallon bottle of neutralizer. 

It is necessary only to fill the burette bottle with neutralizer, 
place it on a small box or shelf at a convenient height, and the 
acid test is ready for iise. 

After carefully mixing the milk or cream, fill the 9 cubic centi- 
meter pipette, emptv it in the cup and add a couple of drops of 
the indicator. If heavy cream is tested, it is preferable to fill the 
pipette again with water, and add the rinsing water to the con- 
tents of the cup. Fill the graduated burette by tipping the bottle 
and place level again. Adjust the burette and rubber stopper so 
that the neutralizer will stand at the zero mark in the burette, then 



54 TESTS FOR ACID IN MILK 

let the neutralize!- run into the cup a little at a time, shaking the 
cup by circular motion, until the contents has attained a pink shade 
and does not turn white again within five to ten seconds. The 
number of cubic centimeters of the neutralizer used will then di- 
rectly show how much acid the milk or cream contained, giving 
it in 0.1 per cent. acid. If 3 cubic centimeters of neutralizer have 
been used, the milk contained two-tenths of one per cent, and if, 
for instance, a sample of cream takes 5.6 cubic centimeters of neu- 
tralizer, it contained 56 hundredths of 1 per cent, of acid, generally 
written as .2 per cent, acid and .56 per cent. acid. To facilitate the 
readings, the burette is graduated in 3/10 of one cubic centimeter 
only, but 1/10 cubic centimeter can easily be read ofif when re- 
quired. As all tests start at the zero mark, there are no calculations 
necessary to determine how much neutralizer has been used, with 
the resulting possible errors. 

Before starting the test, lift the rubber stopper in the neck on 
top of the bottle and replace securely. This operation releases the 
pressure in the bottle, and should be repeated each time the neutral- 
izer does not run freely from the burette. The burette valve is a 
ball valve, and is Avorked by pressing the rubber tubing between 
the fingers. 

Q. Is there a more convenient way to test a great number of 
samples of milk? 

A. If many samples of milk are tested at the receiving plat- 
form with the Marschall test, it is convenient to get a couple dozen 
2 oz. bottles, with wide mouths, and in each fill 2 cubic centimeters 
of neutralizer from the burette, and also a couple of drops of in- 
dicator. The 9 cubic centimeters of the milk taken as sample is 
then simply added to one of the bottles and shaken. If the mixture 
does not tvirn white the milk contains less than .2 per cent. acid. 
This is generally taken as a standard. 

Q. What per cent, of acid will the acid test show in freshly 
drawn milk? 

A. About .07 per cent, due to acid phosphates, free carbonic 
acid gas and an acid reaction of the casein. Lactic acid develops 
after the milk is drawn. 

Q. What is the per cent, of acid in milk when it begins to 
taste sour? 

A. About .30 to .35. 

Q. What amount of acid is allowable in market milk? 

A. Retail milk should contain less than .2 per cent, of acid. 

Milk received at the factories should not contain more than 
.2 per cent, acid, and milk containing .25 per cent, acid and over 
can not be pasteurized. Most butter makers would refuse milk 
showing more than .3 per cent. acid. 

Q. Does a change in the per cent, of acidity change the flavor? 

A. Yes ; the greater the amount of acid developed in cream 
the more sour it will taste. 



PRESERVATIVES 55 

Q. What per cent, of acid should there be in cream for butter 
making? 

A. Cream ready to churn should contain A to .55 per cent, 
acid, according to whether mild or highly flavored butter is wanted, 
and also depending upon the per cent, of fat in the cream. The 
higher the per cent, of fat the less acid is needed. 

Q. What per cent, of acid should there be in starters used for 
butter and cheese making? 

A. Starter for butter or cheese should be used immediately, or 
else cooled down quickly, when it shows .7 to .85 per cent. acid. 

DIVISION SIXTEEN. 

DETECTION OF PRESERVATIVES. 
Q. How may formalin be detected in milk? 

A. To about 10 c.c. of milk in a test tube or in the Babcock 
test bottle, add an equal amount of well water. Pour concentrated 
sulphuric acid down the side of the tube, taking care not to mix 
with the milk. If formalin is present a distinct purple ring will 
form at the junction of the milk and acid. The purpose of the well 
water is to add iron. This may be supplied by adding 4 or 5 drops 
of a 10 per cent, solution of ferric chloride. It will not be neces- 
sary when commercial sulphuric acid is used. 

(b) A more delicate test is made as follows : Prepare a solu- 
tion of concentrated hydrochloric acid (sp. gr. 1.2) containing 3 c.c. 
of 10 per cent, ferric chloride (Fe cl 5) per liter. To 10 c.c. of milk 
add 10 c.c. of this solution in a white dish. Bring slowly to the 
boiling point. If formalin is present a violet color appears. 

Q. How^ may bi-carbonate of soda be detected in milk or 
cream? 

A. To 10 c.c. of milk in a test tube add 10 c.c. of alcohol and 
a few drops of a one per cent, solution of rosolic acid and mix. If a 
carbonate is present a rose red color appears, while pure milk 
shows a yellowish red color. 

Q. How may borax and boracic acid be detected in milk or 
cream ? 

A. Pour 15 or 20 c.c. of milk into a porcelain dish, make it 
alkaline with sodium hydrate, evaporate and burn to an ash. Add 
a few drops of diluted hydrochloric acid to the ash. Soak a strip 
of tumeric paper in this solution and dry with heat. If borax or 
boracic acid is present, the paper will be a distinct cherry red when 
dry and turn olive green on the addition of dilute ammonia. 

DIVISION SEVENTEEN. 
BACTERIA IN MILK. 

Q. What are bacteria? 

A. The lowest form of plant life. They are single celled and 
microscopical. 

Q. How do bacteria reproduce? 



56 BACTERIA IN MILK 

A. By fission or by one bacterium simply dividing into two. 

Q. What are spores? 

A. When some bacteria come under unfavorable conditions 
for grow^th they form spores. A small bright spot appears within 
the bacterium and gradually becomes larger. The old cell breaks 
up and disappears, leaving the spore. This spore is very resistant 
to heat, drying and the various things which usually destroy bac- 
teria. A comparatively small number of different species of bac- 
teria are capable of forming spores. 

Q. What things are necessary to bacterial growth? 

A. Food, moisture, and heat between certain limits. Some 
species demand the presence of air, others the absence of air, while 
still others will grow either in its presence or absence. The com- 
mon lactic acid bacteria which cause milk to sour belong to the 
last class. 

Q. What is the most favorable temperature for bacterial 
growth ? 

A. Most bacteria grow most rapidly between 80° and 100° F. 
Some will grow rapidly between 60° and 70°, the common lactic 
acid bacteria of milk being in this class. Most species are injured 
by a temperature above 100° but a few types will grow at 140° F. 
There is very little bacterial growth below 50° F. 

Q. How may bacteria be killed? 

A. The practical means are heat, direct sunlight and chemical 
disinfectants. 

Q. How much heat is necessary to kill bacteria? 

A. A temperature of 1-10° F. for one-half hour will kill most 
growing bacteria. Higher temperatures will kill them more quick- 
ly. Bacterium tuberculosis is killed b}- 140° F. for 20 minutes. A 
temperature of 160° F. for one minute or less will kill the germs of 
tuberculosis, diphtheria, typhoid and most disease producing germs. 

Q. How may bacterial spores be killed? 

A. By heating under 15 pounds steam pressure for 15 minutes. 
This gives a temperature of about 240° F. Heating in a dry oven 
at a temperature of 300° F. for one-half to one hour will kill them. 

Q. What are some chemical disinfectants? 

A. A 5 per cent, solution of carbolic acid. 
A 1 per cent, solution of mercuric chloride. 
A 5 per cent, solution of formalin. 
Slaked lirrie. 

These are of value in stables and in any place where the milk 
will not come in direct contact with them. 

Q. What is pasteurization? 

A. Pasteurization is the application of sufficient heat to kill 
all growing or vegetative bacteria and then cooling to a low tem- 
perature. Pasteurization does not kill spores. The most satis- 



BACTERIA IN MILK 57 

factory way to pasteurize milk is to heat to 140° F. for 20 to 30 
minutes. 

Q.. What is sterilization? 

A. Sterilization is accomplished by the application of suf- 
ficient heat to kill all bacterial life. It is not practical to sterilize 
milk for market purposes. Heating" under 15 pounds steam pres- 
sure for 15 minutes or steaming for one-half hour on three consecu- 
tive days will sterilize liquids. Glassware and tinware may be 
sterilized by heating under 15 pounds steam pressure for 15 min- 
utes. In laboratory work glassware 'is sterilized by heating to 150° 
C. or 300° F. for one hour in a hot air oven. 

Q. How should milk utensils be washed? 

A. They should first be rinsed in cool or luke-warm water, 
then washed in boiling water containing an alkali, such as bicarbon- 
ate of soda, sal soda or sodium borate. They should then be 
steamed or rinsed with water which has been heated above the 
boiling point for at least one hour. It is very desirable to sterilize 
under 15 pounds steam pressure when this is possible. 

Q. What are the sources of bacteria in milk? 

A. Dirt and dust from the cow, dust in the air, imperfectly 
sterilized utensils, impure water, the hands and clothing of persons 
milking and handling the milk. 

Q. What are the sources of disease germs or bacteria? 

A. The handling of milk by persons diseased or who have 
come in contact with diseased persons ; imperfectly sterilized milk 
bottles or other utensils returned from homes where contagious 
diseases exist; contaminated wash water; diseased cows. 

Q. What means may be employed to secure a low bacterial 
content of milk? 

A. Healthy cows; healthy milkers; clean milkers, both as to 
hands and to clothing; clean cows; clean stables; brushing cows 
and cleaning stables long enough before milking to allow the dust 
to settle, handling hay and bedding after milking and not before; 
wiping the cow's udder and flanks with a damp cloth before milk- 
ing; washing the udder with soap and water when badly soiled; 
using small top milk pails ; using clean sterilized utensils ; cooling 
milk below 50° F. as soon as milked and keeping it cool. 

Q. What are the effects of bacteria on milk? 

A. The most common efifect is the souring of milk by the 
lactic acid bacteria which produce lactic acid from the milk sugar. 
Others produce gas which is troublesome to cheese makers. Still 
other effects are the production of sweet coagulation, the produc- 
tion of undesirable flavors, the production of ropy or slimy milk, 
the production of abnormal color. 

Q. Are all bacteria harmful to milk? 

A. No. Some varieties are neutral or have no effect. The 
lactic acid are of great value to the butter maker, cheese maker and 



58 FERMENTATION TESTS 

maker of fermented milks. When lactic acid bacteria are develop- 
ing they tend to check the growth of undesirable species. 

Q. What is a starter and how made? 

A. A starter is a culture of lactic acid bacteria in milk. It 
may be made by letting clean milk sour naturally at a temperature 
of about 65° F. It may be made from a commercial or pure culture 
of lactic acid bacteria secured from various firms which prepare 
them. The starter may be made from the same by pasteurizing one 
quart of milk at 180° F. for 30 minutes and cooling to 65° F. Then 
add the pure culture and hold at 65° F. until curdled. This will 
not have the good flavor desired but may be used to inoculate a 
second culture prepared in the same manner. This and following 
cultures will have a clean acid flavor if proper care has been used 
to prevent contamination. 

DIVISION EIGHTEEN. 

FERMENTATION TESTS. 
Q. What are fermentation tests of milk? 

A. Tests in which fermentation is allowed to take place in the 
milk or the curd to detect bad flavors, odors and gas production. 
They are of special value to cheese factories and milk dealers for 
testing out the milk of different patrons and to dairymen for test- 
ing the milk of different cows. 

Q. How may the Gerber fermentation test be made? 

A. Secure samples of the milk to be tested in sterile bottle 
with stoppers or caps. Warm to from 98° to 104° F. and hold at 
that temperature until curdled, by placing in water bath. The 
length of time required to curdle, the odors developed and presence 
or absence of gas holes in the curd will indicate the quality of the 
milk. 

Q. How may the curd test be made? 

A. Secure samples of tlie milk to be tested in sterilized wide 
mouth bottles fitted with a cover. At least one-half to two-thirds 
of a pint of milk should be used for each test. Warm the milk to 
98° F. and add about 10 drops of rennet to each bottle. Mix by 
giving the bottle a rotary motion and let stand until curdled, which 
will be about 20 minutes. Cut the curd into small cubes, using a 
clean, sterile case knife. Stir occasionally for 30 to 45 minutes to 
keep the curd from matting and then pour off the whey. It will 
be removed more completely by pouring it off two or three times. 
Then set the bottles in water which should be kept at 98° F. for 6 
to 12 hours. The quality of the different milks will be indicated 
by examining the different curds for odors and by cutting through 
them with a knife, noting the gas holes. Gas should not form in 
the curd of sweet milk. 



RENNET 59 

DIVISION NINETEEN. 

RENNET. 
Q. What is rennet? 

A. An extract obtained from the fourth stomach of a young 
calf. It is supposed to contain enzymes, rennin and pepsin. The 
former has a coag-ulating- action on milk casein and the latter a 
digesting action. 

Q. For what is rennet used? 

A. For precipitating the casein of milk in cheese making. 

Q. Does the curd thus formed contain constituents other than 
casein? 

A. Yes. It contains water, the greater part of the butter fat 
of the milk, a small amount of milk sugar, albumen and ash. 

Q. What factors influence the action of rennet? 

A. It acts most satisfactorily for cheese making at 86° to 
87° F. Increase of temperature hastens and decrease of tempera- 
ture retards its action. Rennet extract is rendered inactive if ex- 
posed to a temperature of 140° F. for some time. Weak solutions 
are afifected by a temperature as low as 105° F. Generally speak- 
ing the greater the acidity the more rapid the action of acid on 
milk. It acts slowly if at all on pasteurized milk, because the 
soluble calcium salts have been precipitated. 

Q. What is the action of rennet in cheese ripening? 

A. The pepsin aids in breaking down the casein into more 
soluble compounds. 

DIVISION TWENTY. 

FEDERAL STANDARDS FOR DAIRY PRODUCTS. 

The following are the standards for milk and its products as 
given in Circular No. 19, Standards of Purity for Food Products, 
U. S. Department of Agriculture. 

Milk is the fresh, clean, lacteal secretion obtained by the com- 
plete milking of one or more healthy cows, properly fed and kept, 
excluding that obtained within fifteen days before and ten days 
after calving, and contains not less than eight and one-half (8.5) 
per cent, of solids not fat, and not less than three and one-quarter 
(3.25) per cent, of milk fat. 

Blended milk is milk modified in its composition so as to have 
a definite and stated percentage of one or more of its constituents. 

Skim-milk is milk from which a part or all of the cream has 
been renioved and contains not less than nine and one-quarter 
(9.25) per cent, of milk solids. 

Pasteurized milk is milk that has been heated below boiling 
sufficiently to kill most of the active organisms present and im- 
mediatelv cooled to 50° F. or lower. 

Sterilized milk is milk that has been heated to the temperature 



60 FEDERAL STANDARDS 

of boiling water, or higher for a length of time sufficient to kill all 
organisms present. 

Condensed milk, evaporated milk, is milk from which a con- 
siderable portion of water has been evaporated and contains not 
less than twenty-eight (28) per cent, of milk solids of which not 
less than twenty-seven and five-tenths (37.5) per cent, is milk fat. 

Sweetened condensed milk is milk from which a considerable 
portion of the water has been evaporated and to which sugar 
(sucrose) has been added, and contains not less than twenty-eight 
(28) per cent, of milk solids, of which not less than twenty-seven 
and five-tenths (27.5) per cent, is milk fat. 

Condensed skim-milk is skim-milk from which a considerable 
portion of the water has been evaporated. 

Buttermilk is the product that remains when butter is re- 
moved from milk or cream in the process of churning. 

Goat's milk, ewe's milk, etc., are the fresh, clean, lacteal secre- 
tions, free from colostrum, obtained by the complete milking of 
healthy animals, other than cows, properly fed and kept, and con- 
form in name to the species of animal from which they are obtained. 

Cream is that portion of milk, rich in milk fat, which rises to 
the surface of milk on standing, or is separated from it by centrif- 
ugal force, is fresh and clean and contains not less than eighteen 
(18) per cent, of milk fat. 

Evaporated cream, clotted cream, is cream from which a con- 
siderable portion of water has been evaporated. 

Milk-fat, butter-fat is the fat of milk and has a Reichert-Meis- 
sel Number not less than twenty-four (2-i) and a specific gravity 
(40° C.) 

not less than 0.!)05 ( ) 

(40° C.) 

*Butter is the clean, non-rancid product made by gathering 
in any manner the fat of fresh or ripened milk or cream into a mass, 
which also contains a small portion of the other milk constituents, 
v/ith or without salt, and contains not less than eighty-two and 
five-tenths (82.5) per cent, of milk fat. By acts of Congress ap- 
proved August 2. 1886, and May 9, 1902, butter may also contain 
added coloring matter. 

Renovated butter, process butter, is the product made by melt- 
or any substance except milk, cream, or salt, and contains not more 
ing butter and reworking, without the addition or use of chemicals 
than sixteen (16) per cent, of water and at least eighty-two and 
five-tenths (82.5) per cent, of milk fat. 

*The inspection of butter and renovated butter is done by the 
Internal Revenue Department. All butter containing 16 per cent. 
of moisture or more is classed as adulterated butter by the Internal 
Revenue law. If it is otherwise entitled to the name, it will pass 
inspection if it contains less than 16 per cent, of moisture. 



FEDERAL STANDARDS 61 

Cheese is the sound, soHd and ripened product made from milk 
or cream by coagulating the casein thereof with rennet or lactic 
acid, with or without the addition of ripening ferments and season- 
ing, and contains, in the water-free substance, not less than fifty 
(50) per cent, of milk fat. By act of Congress, approved June G, 
1906, cheese may also contain added coloring matter. 

Skim-milk cheese is the sound, solid and ripened product made 
from skim-milk by coagulating the casein thereof with rennet or 
lactic acid, with or without the addition of ripening ferments or 
seasoning. 

Goat's milk cheese, ewe's milk cheese, etc., are the sound, rip- 
ened products made from the milks of the animals specified, by 
coagulating the casein thereof with rennet or lactic acid, with or 
without the addition of ripening ferments and seasoning. 

Ice cream is a frozen product made from cream and sugar, 
with or without a natural flavoring, and contains not less than 
fourteen (14) per cent, of milk fat. 

Fruit ice cream is a frozen product made from cream, sugar, 
and sound, clean, mature fruits, and contains not less than twelve 
(12) per cent, of milk fat. 

Nut ice cream is a frozen product made from cream, sugar and 
sound, non-rancid nuts, and contains not less than twelve (12) per 
cent, ot milk fat. 

Whey is the product remaining after the removal of fat and 
casein from, milk in the process of cheese-making. 

Kumiss is the product made by the alcoholic fermentation of 
mare's milk or cow's milk. 

Tli(^ standard for unsweetened evaporated or condensed milk as 
given on page 60 has recently been changed by Food Inspection Decision 
No. 131, as follows: 

"(1) It should be prepared by evaporating the fresh, pure, 
whole milk of healthy cows, obtained by complete milking and exclud- 
ing all milkings within 15 days before calving and 7 days after calving 
provided at the end of this 7-day period the animals are in a perfectly 
normal condition. 

(2) It should contain such percentages of total solids and 
of fat that the sum of the two shall be not less than 34.3 and the per- 
centage of fat shall be not less than 7.8 per cent. This allows a small 
reduction in total solids with increasing richness of the milk in fat. 

(3) It should contain no added butter or butter oil incor- 
porated either with whole milk or skimmed milk or with the evaporated 
milk at any stage of manufacture." 



62 NOTES 

DIVISION TWENTY-ONE. 

LABORATORY EXERCISES 

GENERAL DIRECTIONS. 

1. Each student must be supplied with a dairy outfit. The 
key for the locker containing- the same may be secured from the 
chemical store room 'after the laboratory deposit has been made 
and assignment received from the instructor in charge. 

2. Each student must be supplied with a white suit for 
laboratory work. 

3. Each student must clean his desk and all apparatus used 
by him before leaving the laboratory, 

4. The breakage or loss of any glassware or other apparatus 
placed in the laboratory for general use will be charged to the class 
as a whole unless replaced by the student responsible. 

For references read : Farrington and Woll's "Testing Milk and 
its Products ;" Van Slyke's "Modern Methods of Testing Milk and 
Milk Products." 



EXERCISE I. 

Check all glassware and report at once any missing or broken 
pieces. Wash all glassware in hot water, using Wyandotte Wash- 
ing Powder. 

A good solution for occasional use in cleansing glassware is 
made by dissolving 1 pound of potassium bichromate in 1 gallon 
of sulphuric acid. This may be diluted with water or used full 
streneth. 



NOTES 63 

EXERCISE II. 

CALIBRATION. 

For methods see Division 7. 

(a) Calibrate all whole milk bottles with the plunger or 
Trowbridge Calibrator. 

(b) Calibrate skim-milk bottles by the use of mercury. 

(c) Calibrate cream bottles and pipettes by the use of burette 
and distilled water. 

Report all inaccurate pieces to instructor in charge. 
Record all pieces calibrated and results. 



C4 LABORATORY EXERCISES 

EXERCISE III. 

TESTING WHOLE MILK. 

For method see Division 7. 

(a) Test a sample of milk in duplicate (using two bottles). 

(b) Test another sample of whole milk in duplicate. 

In each case read the fat column immediately on taking from 
centrifuge. Then place in water at temperature of 140° for 4 min- 
utes and read again. Let the bottles stand at room temperature 
and take readings every ten minutes until the fat solidifies. 

Record the test of each bottle at the three different readings. 
If the per cent, in duplicate bottles when read from the hot water 
bath varies more than .2 per cent, test must be made again. This 
rule will hold in all Babcock tests for milk. 

What is the color of the fat column and other contents of the 
bottle? 

Record any other facts noted. 

Problems. — How many pounds of butter fat in 475 pounds of 
the milk tested in (a) ? 

How many pounds of butter fat in 360 gallons of the milk test- 
ed in (a) ? 

Solve the same problems for the milk tested in (b). 



NOTES 65 



66 LABORATORY EXERCISES 

EXERCISE IV. 

EFFECT OF DIFFERENT AMOUNTS OF ACID AND 

DIFFERENT TEMPERATURES ON THE 

BABCOCK TEST. 

Make 7 duplicate tests of a sample of whole milk as follows : 

(a) Use the regular amount of acid. 

(b) Use one-half the usual amount of acid. 

(c) Fill the bowl nearly to base of neck with acid. 

(d) Warm both milk and acid to 110° F. before mixing. Use 
the usual amount of acid. 

(e) Cool both milk and acid to 40° F. before testing. 

(f) Test milk as usual but use chemically pure acid instead of 
the commercial. 

(g) Very carefully add 2 or 3 cubic centimeters of water to 
17.5 c.c. of commercial acid. Use 17.5 c.c. of this mixture in mak- 
ing one test. 

Record the per cent, of fat in each bottle, the color of the fat 
column in each case and any other differences you may note. 



NOTES 



67 



68 LABORATORY EXERCISES 

EXERCISE V. 

COMPARISON OF STEAM AND HAND TESTERS AND 
DIFFERENT SPEEDS OF TESTER. 

(a) Test a sample of whole milk in duplicate in power tester. 

(b) Test same milk in duplicate in hand tester. 

(c) Test same milk in duplicate running at one-half usual 
speed. 

(d) Test in duplicate a sample of skim-milk. 

Record the test of each bottle and note any differences between 
tests in hand and power testers and at different speeds. 



NOTES 69 



70 LABORATORY EXERCISES 

EXERCISE VI. 

SKIM-MILK AND CREAM TESTING. 

For methods see Divisions 8 and 9. 

(a) Test a sample of skim-milk, using two whole milk and 
two skim-milk bottles. Note and record results from both kinds 
of bottles. 

(b) Test a sample of cream in duplicate using 9 grams in 
9-gram bottles. 

(c) Test the same cream in duplicate, using 9 grams of cream 
in 18-gram bottles. What must be done to the fat reading when 
using 9 grams of cream in an 18-gram bottle? 

Use glymol in reading cream tests. 

Record results in full in regard to per cent, of fat, color of 
fat column, etc. 

Problems. — (a) How many pounds of butter fat in 650 pounds 
of the above cream? 

(b) How many pounds of butter fat in 300 gallons of the 
above cream? 

(c) How many pounds of butter fat were lost in 600 pounds 
of the above skim-milk? 



NOTES 71 



72 LABORATORY EXERCISES 

EXERCISE VII. 

CREAM TESTING. 

(a) Test a sample of cream in duplicate in O-gram 50 per 
cent, bottles. 

(1) Read the per cent, of fat directly after the tester 
has stopped. 

(2) Place in hot water at a temperature of 140° F. for 
4 minutes and read again, placing back into the 
water. 

(3) Add glymol to top of fat column and read again. 

(b) Test the same cream, using 18 grams in an 18-gram cream 
bottle. Follow out (1), (2), (3) as above. 

(c) Test a sample of buttermilk in duplicate using skim- 
milk bottles. 

Record results in detail. 

Show the number of pounds of butter fat a creamery would 
pay for in buying 464 pounds of cream by the different readings of 
per cent, of fat in the above experiment. 



NOTES 73 



74 LABORATORY EXERCISES 

EXERCISE VIII. 
TESTING CREAM, BUTTERMILK AND SKIM-MILK. 

(a) Take a sample of cream from a cream can and test it 
for butter fat. 

What precautions are necessary to get a fair sample of cream 
from the can? See Division 9. 

How much butter can be made from 100 gallons of this cneam 
if the overrun is 18 per cent.? 

(b) Test a sample of buttermilk for butter fat using 2 whole 
milk and 2 skim-milk bottles. 

How much butter fat did the butter maker lose in 840 pounds 
of this buttermilk? 

(c) Test a sample of skim-milk in 2 skim-milk and 2 whole 
milk bottles. 

What was the loss of butter fat in 9-10 pounds of this skim- 
milk? 



NOTES 



7J 



76 LABORATORY EXERCISES 

EXERCISE IX. 

TESTING BUTTER. 

For methods see Division 10. 

(a) Prepare a sample of butter for testing. 

(b) Test for butter fat using- two cream bottles and one spe- 
cial butter test bottle. 

(c) Make 3 tests of the same butter for moisture b}^ the 
Irish method. 

(d) Test the same butter for salt, making 3 titrations of the 
salt solution. 

(e) If your tests are correct what is the per cent, of consti- 
tuents other than salt, water and butter fat in this butter? 

How near to the legal limits are the per cents, of water and 
butter fat? 



NOTES 7? 



78 LABORATORY EXERCISES 

EXERCISE X. 
TESTING CHEESE. 

For methods see Division 10. 

(a) Secure a sample of several different kinds of cheese. Take 
three small pieces of each and put into as many test tubes. Then 
add a few c.c. of water to one of each kind, a few c.c. of sulphuric 
acid to one of each kind, a few c.c. of hydrochloric acid to one of 
each kind. Note the effect of the different solvents on the different 
kinds of cheese during the class period and set away until the next 
period and examine again. 

(b) Test a sample of cheese for moisture. 

(c) Test the same cheese in duplicate for butter fat. 

(d) Test a sample of whey for butter fat, using 3 whole milk 
and two skim-milk bottles. 

(e) How much butter fat was lost in 560 pounds of this whey? 



NOTES 79 



80 LABORATORY EXERCISES 

EXERCISE XI. 

TESTING CONDENSED MILK AND ICE CREAM FOR 
BUTTER FAT. 

For methods see Division 11. 

(a) Test a sample of ice cream in duplicate. 

(b) Test one bottle of ice cream in same manner as ordinary 
cream and compare results with (a). 

Why does (b) not give good results? 

(c) Test a sample of unsweetened condensed milk in dupli- 
cate. 

(d) Test a sample of sweetened condensed milk in dupli- 
cate. 



LABORATORY EXERCISES 81 

EXERCISE XII. 
ACIDITY TESTS. 

For methods see Division 14. 

(a) Test a sample of sweet milk for acid by both Mann's and 
Marschall's tests, making two determinations by each method. 

(b) Repeat (a) with sour milk. 

(c) Repeat (a) with sweet cream. 

Be sure to rinse the pipette with distilled water when testing 
cream, running the rinsings into cup with the cream. 

(d) Repeat (a) with sour cream. 

(e) Repeat (a) with buttermilk. 

(f) Repeat (a) with some milk soured by Bacillus Bul- 
garicus. 



82 NOTES 



LABORATORY EXERCISES 83 

EXERCISE XIII. 
THE USE OF THE LACTOMETER. 

For methods see Division 13. 

(a) Make the following determinations with a sample of milk 
and in the order given : (1) Per cent, of fat. (2) Lactometer read- 
ing. (3) Temperature of milk. (4) Lactometer reading corrected 
to 60° temperature. (5) Specific gravity of the milk. (G) Per cent, 
of solids not fat. (7) Per cent, of total solids . (8) Specific gravity 
of the total solids. 

(b) Add 10 per cent, of water to the above milk and again 
make the same determinations. 



84 



NOFRS 



LABORATORY EXERCISES 85 

EXERCISE XIV. 

DETECTION OF ADULTERATION. 

Test four different samples of milk in same mannei as in Ex- 
ercise XIII. 

Determine which samples are adulterated and in wlial manner 
See Division 13. 



86 NOTES 



LABORATORY EXERCISES 87 

EXERCISE XV. 
HART CASEIN TEST AND FERMENTATION TESTS. 

For methods see Divisions 10 and 17. 

(a) Test in duplicate a sample of whole milk for butter fat. 

(b) Test the same milk for casein by the Hart Casein Test. 

(c) At the beginning- of laboratory period sterilize two pint 
bottles for fermentation tests, by putting them in autoclave under 
15 pounds steam pressure for 15 minutes. When bottles have 
cooled prepare sample of milk for Gerber fermentation test in one 
and for curd test in the other. Examine on the two following days 
for odors and gas production. 

( d) How much cheese per hundred pounds may be made from 
the milk tested in (a) and (b) ? Use both formulas given. 



88 



NOTES 



LABORATORY EXERCISES 89 

EXERCISE XVI. 

PRESERVATIVES. 

For methods see Division 15. 

(a) Test each of the samples of milk provided for formalde- 
hyde, borax or boracic acid, and sodium carbonate. 



90 LABORATORY EXERCISES 

EXERCISE XVII 

DETECTION OF OLEOMARGARINE AND RENOVATED 

BUTTER. 

For methods see Division 10. 

(a) Examine the samples of material furnished and determine 
which are butter, which are oleo and which renovated butter. 

(b) Test one sample of each product for moisture, by one of 
the tests given for determining moisture in butter. 



LABORATORY EXERCISES 91 

EXERCISE XVIII 
COMPOSITE TESTS. 

See composite tests under Division 7. 

(a) Test for butter fat each of 9 samples furnished. Divide 
the 9 samples into three groups of three each. Take three com- 
posite samples, one from each of the three groups at the rate of 1 c. 
c. for each pound of milk represented by the different samples. The 
pounds of milk will be noted on the label of each sample. 

Place a corrosive sublimate preservative tablet in each com- 
posite sample, shake until dissolved, stopper tightly and set aside 
until next period for testing. 

(b) Determine the number of pounds of fat in the milk repre- 
sented by each of the above samples. Determine the average per 
cent, of fat in the 9 samples and the average per cent, in each of 
the groups. Compare these averages with the tests of the com- 
posites at the next period. 

(c) Beside the composite samples tightly stopper two other 
samples and set away without preservative until the next testing- 
period. Record the tests of these samples to be compared with 
their tests at the next period. 



NOTES 



LABORATORY EXERCISES 93 

EXERCISE XIX. 

TESTING COMPOSITE SAMPLES AND CREAM. 

(a) Test the three composite samples saved from last period 
and compare tests With average of the individual tests. 

(b) In taking these composite samples, why was it necessary 
to take them- proportionately, or 1 c.c. for each pound instead of 
an equal amount, such as 15 c.c. from each sample? 

(c) Test the two samples held over from last period without 
preservative. If they are curdled, test as recommended for curdled 
milk in Division 7, and compare per cent, of fat with that obtained 
in former tests. 

(d) Test a sample of cream for butter fat in duplicate. 



04 LABORATORY EXERCISES 

EXERCISE XX. 

EXPERIMENTS WITH RENNET. 

Note Division 18. 

Dilute some rennet by putting 5 c.c. of rennet into a 50 c.c. 
glass flask and filling the flask to the mark with water. 

(a) Warm some sweet milk to 86° F. Add two 17.6 c.c. pi- 
pettefuls to a beaker or porcelain cup. Add one cubic centimeter 
of the dilute rennet and give a quick stir with the thermometer or 
shake the beaker in such manner as to give contents a rotary mo- 
tion. Note the length of time it takes to coagulate. 

(b) Repeat the experiment with milk just beginning to taste 
sour or add a small amount of very dilute hydrochloric or sul- 
phuric acid to the milk. 

(c) Repeat with milk neutralized with sodium hydroxide. 

(d) Repeat (a) with sample of the original milk at 95° F., 
106° F., 120° F., 140° F., 70° and 60° F. 

(e) Repeat (a) with the same milk diluted at the rate of 1 
part water to 3 of milk. 

(f Repeat (e) with 1 part water and 2 parts milk, 
(g) Repeat (e) with 1 part water and 1 part milk. 



NOTES 95 



96 LABORATORY EXERCISES 

EXERCISE XXI. 

Effect of salt and soluble salts on rennet. 

(a) Action. — Make a test of rennet action as in (a) Ex. 20. 

(b) Repeat (a) with the same milk, three times, adding one 
per cent, of salt to the milk in the first, 3 per cent, in the second 
and 5 per cent, in the third test. 

(c) Repeat (a) with the same milk, adding a small amount 
of dilute solution of calcium chloride. 

(d) Repeat (a) with milk heated to 190° F. for 10 minutes and 
cooled to the usual temperature of 86° F. 



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